Just figured I'd throw together a quick guide for this game because there wasn't one already... or at least not in English. There is a Chinese one, and very little else besides. The boards have basically no relevant information so the most I could do is reference Jessie's Quest Guide and extrapolate what I could from the Chinese guide via translation.

I will give moderate instructions for getting an achievement if I believe it is obscure or uncertain and info isn't sufficiently available elsewhere, but I have no intention of making a full guide for Hard Mode nor duplicating the efforts of Jessie's Quest Guide by hand-walking anyone through quests.
I'm not 100% sure in some cases whether achievements are missable or not, but I'm moderately sure some of them are.

NOTE: I don't believe the Steam Overlay thing works for this game, so there won't be a pop-up when you get achievements. You will see them appear pretty much instantly in Steam's Library section against the game though.

Just a bunch of Achievements tied to the completion of Guild Quests or general story progression.
If you need to know how to unlock a particular quest then open up the menu in-game and go to System > Flow Chart. The lines directly indicate prerequisites for each quest. Once you've met the prerequisite then the Quest will either be given at the Guild Counter or by some NPC hanging around the world with a big QUEST sign over their head.
If you need further info then reference Jessie's Quest Guide.


Just complete Beginner's Cave and return to the Guild.
Not Missable.



After getting the guild card, follow the advice given and return to the back of Beginner's Cave to the doors that were locked before. A bunch of cutscene stuff happens and eventually you meet Granma. Cheevo get.
Not Missable.



Quest 4 will send you off to exterminate rats in some dude's basement in the Outskirts.
Just beat the Rat Boss at the end of the tunnel to get the cheevo.
Not Missable, though the dungeon itself becomes inaccessible afterwards.



You get this cheevo when you start Quest 5.
Not Missable.


The first quest not given by the guild. Requires you complete the first few guild quests first. Speak to the kid by the well in town to get the quest. His first two hiding spots are pretty obvious from the hints: the Weapon Shop and the Guild. His 3rd hiding spot is Love Park, for which he gives no clue whatsoever. Little bastard.
Not Missable... probably.


Quest 14 is given by the blacksmith guy with goggles right in front of you in the entry area to Eldia after you've completed Quest 13. He will give you a sword called Avenger. What you need to do is equip Avenger on any character and go fight 200+ battles. You don't need to hit anyone with the sword, though it can't hurt your progress. It just needs to be equipped by someone in 200+ battles.
If you're having trouble keeping track of how many battles you've fought with it, you can go back to the blacksmith and talk to him to get your battle count with the sword without handing the quest in. All the same I'd recommend saving the game before talking to him just in case you screw up.
This quest isn't the prerequisite for anything else so you can take your time and advance the rest of the game freely if you want.
Very Much Missable
(Sneaky Tip: If by some shenanigans you end up with multiple copies of Avenger, you can equip them to different characters and it will count every battle once per copy of the sword. With 2 copies you only need to do 100 battles, for instance.)


An easy quest to overlook. This one is given by an NPC at the top of Mt. Megalith, and the QUEST icon should be visible on the World Map once you meet the requirements (I believe you just need to have done Quest 26). Just nip up to him, get Quest 27, find the 3 cards nearby and return to him to complete it and get the cheevo. Note the Resurrection Card thingie he gives you will be important for Quest 32 so hold onto it.
Not Missable... I think.


For Quest 33 you will have to crush a nest full of Giant Ants in the village of Maitsu. Defeating the Final Boss of the dungeon (the Ant Queen) will net you this cheevo. Don't forget to get the Formation Scroll for the Prince Guard formation while you're down there.
Maybe Missable. The Dungeon becomes inaccessible at the end of the quest and the option to collapse the tunnel was there at the start. I just didn't try it.


Quest 35 is a pain to find. I believe you need to have done Quest 31 and maybe Quest 34. Go to the middle house in the Eldia Residential District (next to the orange-haired girl) and you should see a woman beside a girl in the bed. Try to talk to the woman. THEN go to the Guild to pick up the quest. It is a long and convoluted quest, and I suggest you reference the Quest Guide to figure it out if you get stuck... but basically when you defeat the final Dream Eater boss, this cheevo procs.
Not Missable... probably, since it seems to be a prerequisite for the end-game.


Both of these quests reference the official "final boss" of the game (though it should be pretty obvious there is more to the game than that). To get both cheevos you should ideally be doing the entire game on Hard difficulty (which you should have selected at the start and never changed). I've read a few accounts on the boards about fiddling the difficulty before this point and still getting the cheevo, but I didn't really understand what they were getting at and wasn't going to risk it (this game is VERY grindy sometimes). I did the game on Hard. I will NOT advise you on how to play the game on Hard. Figure that out yourself. However this is the only difficulty-locked cheevo, so once you've beaten The Countess (both forms) then you can lower the difficulty if you want.
"He who shall not be named" is not missable.
"The Prince of Island SAGA" is Definitely Missable


To get this cheevo you need to complete Quest 50, retrieve the "Harem Harem" item from the super secret final dungeon that fairy queen Titania lets you into, and then slot it into the device at the top of Mt. Pachika along with the "Love Rheid". You'll have to confirm a few times since this is absolutely the end of the game, but select "I want the four girls with me" to get the harem ending and the cheevo. Go check the Quest Guide if you want detailed instructions on how to do this.
This achievement is Probably Missable... I mean it wouldn't be a Secret Ending if there weren't other lesser endings that could prevent you getting it, would it?

After you've completed the Beginner's Cave and got the Guild Card, look outside the Guild Building just to the left. There should be a cat by the wall. Select the option to pet the cat for the cheevo.
Not Missable.


You need to go around the Adventurers Guild and talk to all the Adventurers there and specifically ask them for tips (rather than making pervy comments). That is to say all of the girls AND the one guy with the green beard. The guy I believe you have to say you're "not interested in guys" or somesuch and he'll tell you a tip. As you progress through guild quests the adventurers present in the room will change. You should be able to get this pretty early in the game, but it might take a few quests for you to talk to all of them.
Missable ... because once you've got the Love Rheid (Q40 outcome) the Adventurers won't give tips any more.


After getting the Guild Card from the Beginner's Cave or any time after that, go to Eldia's Magic District and step into the Dojo. Speak to any of the coloured grannies and select to teach magic to the Prince. Easy cheevo. I'd recommend Light Magic for thematic reasons, but also because Light Magic gets an AoE instant-kill attack at higher levels. It is silly powerful.
Not Missable.

Combination Attacks should happen naturally as you progress through the game. Any Technique or Spell besides basic weapon attacks or punches can chain into any other. It isn't difficult to get them sometimes, though how often they happen and how many of the girls join in is a matter of RNG. Still, you should have both these cheevos by the end of the game even if you never use any accessories that boost the odds.
Obviously these cheevos are Not Missable.


Okay... this one is tricky. You need to proc a Combination Attack with all 5 characters. If you get a 2 or 3 character combination you'll just see their face come up in a bar (except the Prince). If you get a 4 character combination you'll get a full torso shot bar with a breast-jiggle. You'll know you got the 5 character combination because you'll get a full screen team torso shot with synchronised breast-jiggle.
In the entire time I played the game I only got this to happen ONCE naturally without any accessory boosts. It is pure RNG... but there are some items you can equip to help things along.

• Combo Ring boosts Combination Attack Chance by 10% and can be bought from the Accessory Shop later in the game for 1000 gold each.
  
• Super Combo Ring boosts Combination Attack Chance by 30% but I finished the game without seeing any, so they're probably just random RNG chest crap.
  
• Connected Love boosts Combination Attack Chance by 100%, and you'd figure by the unique name and icon that it would be some sort of quest item... but I never saw one naturally.

Personally my approach for getting this as quickly as easily as possible is to buy 20 Combo Rings from the Accessory Shop as soon as they become available then equip 4 of them on every character. Make sure you've done enough "Martial Arts" to have the Kick technique unlocked. It shouldn't cost anything to use, triggers very quickly, and can be used for Combination Attacks. It also helps to have the Earth Magic spell Berserk as that also increases odds. Sakura knows Earth Magic from the beginning but anyone can be taught the spell from level 1.
What you want to do is go up against a large group of physically resistant enemies (like the Sewer Slimes), cast Berserk on everyone, then just have everyone spam Kick. If it works out you'll trigger the rare and elusive combination attack Kick Kick Kick Kick Kick... which is every bit as silly as it sounds, but not quite as silly as the even more rare and elusive Thumbing Thumbing Thumbing Thumbing Thumbing.
Not Missable in any case, but you might need a lot of grinding to manage it.

Tech Sparks are where you try to use a weapon (or unarmed) attack in combat and the character has a little flash and uses a completely different move instead, which is them learning a new Technique.
So far as these three cheevos are concerned you can just learn any 30 new techniques for any character. It really doesn't matter which. This will probably happen naturally as you progress through the game and definitely as you get the other weapon technique / skill cheevos.
These three cheevos are Not Missable.

There are some things worth noting though:
#1. Tech Sparks can trigger from both regular Weapon Attacks and other Techniques. They do NOT trigger from Magic Spells. I'm not 100% sure on this, but I believe regular weapon attacks have higher odds of triggering one... but then again you'll be using more of those than anything else over the course of the game. You can also get a Tech Spark in the middle of a Combination Attack with very little warning.
#2. Tech Spark probability seems to scale with the scaling of the enemies you're attacking. i.e. You'll get them a lot faster when attacking stronger enemies with a new weapon type.
#3. The probability of getting given Techniques does NOT seem to be tied to Weapon Level at all. In fact I'm not even sure if Weapon Level does anything at all. As far as I can tell there is a fixed probability for unlocking any given technique with any given attack, with stronger techniques having lower probabilities.
#4. I don't believe Techniques have prerequisites besides attacking with the relevant weapon. You certainly don't need to unlock the weaker attacks before the stronger attacks. It just happens randomly, like so many other things in this game. That said, I'm pretty sure you can only get one Tech Spark per character per turn.
#5. You almost certainly won't have all the Techniques for a given weapon by the end of the game. All the RNG crap combined with the constant stat gains and the enemy scaling cap more or less ensure that by late game you will be doing fewer and fewer attacks per fight with fewer chances to proc the extremely low odds of a given Tech Spark.

So that brings us to specific techniques...


The easiest of the weapon technique achievements. Also the only hidden one for some reason. Cut Timber is an Axe technique so equip a character with any Axe and get them chopping. It should be one of the first techniques unlocked since it only costs 2TP, but if you're having difficulty then get more axes and equip them on more characters.
Not Missable.


This one is a little trickier. You're after the 9TP Greatsword technique Swallow Reversal. In case it isn't obvious, there are two types of swords and you want the type that can't be used with shields. Equip a character with any Greatsword and keep attacking for the duration of the game. You should get it eventually without too much trouble. But again, if you're having trouble then stick Greatswords on everyone and set them all to grinding Slimes in the Sewer dungeon.
Not Missable.


Shooting Star is the ultimate 14TP Spear technique. This achievement is one of the worst grinds in the entire game. I spent many many hours grinding Slimes in the Sewer dungeon with all 5 characters using Spears (and given the RNG nature of equipment gains, they were shop-bought weak spears) and everyone was Spear level 27 by the time Iris alone finally managed to unlock the technique and bring the all-spear insanity to an end. The monster scaling actually capped out while I was doing this, and regular monsters had all become orders of magnitude stronger than the bosses.
Technically not Missable, but you could grind this for so long without getting it that you start to question if the game is gaslighting you.


Another ultimate technique, this time for "Martial Arts" (i.e. unarmed attacks). Thousand-Hand Bodhisattva is probably the most powerful technique of any sort in the entire game (very useful for super powerful bosses) and costs a whopping 20TP to use. Fortunately you do NOT need specific gear to grind this one out. Still, expect it to take almost as long as the spear tech before. Insanely grindy. By the end of the game I'd been able to unlock this technique for 3 characters. I was trying for all 5 but I couldn't do it.
Again, Technically not Missable, but insanely grindy and even if you spend forever grinding everyone for it you'd be lucky to see it more than once.


This one is a little different. While weapon levels don't seem to make any difference to anything as far as I can tell, Magic Element Levels determine which spells you can learn from the grannies in the Dojo in the Magic District, up to presumably a maximum at Level 30 (I didn't honestly check). For this cheevo in theory you just need to get any magic school on any character up to Lv.30... but for me it didn't proc the first time (Nadia's Fire Magic), so I had to grind up a second (Iris's Wind Magic).
From what I've seen regarding both Weapon Levels and Magic Levels though, the more levels you've gained already in any weapon or magic type, the more grinding you need to do in order to raise other levels in other things. And because I'd already done the grinding for weapon techniques before even trying to level up magic (which is why everyone was Lv.27 in the Spear and Lv.30+ in Martial Arts), it became a considerable grind to get everyone's element levels up toward 30. If you spread yourself too thin, you're just making life more difficult for yourself later... so it MIGHT be best to handle this achievement before the weapon technique cheevos.
It doesn't help that it also takes more side-scrolling through menus per character than weapons.
Not Missable.

Pretty early in the game you should get the book / scroll for the formation Love Wall. I believe it might have been in Beginner's Cave, but I don't remember precisely. If you take the item to the old man just inside Beginner's Cave and talk to him, he'll unlock the formation for you and you'll get the cheevo.
Not Missable, I believe.


You get this formation scroll for the Prince Guard formation from the ant tunnels during Quest 33. It is just lying on the ground on a square patch of ground in one of the later areas of the dungeon, after one of the girls comments about ant eggs. Very easy to miss, and the dungeon gets collapsed after the quest, so if you don't have it by the time you've beaten the Ant Queen, I recommend thoroughly searching the dungeon before leaving.
Once you have the scroll and have left, return to Beginner's Cave and speak to the old man just inside the cave to learn the formation and get the cheevo.
VERY MISSABLE.


After you complete the chain of Quests 46, 47 and 49, you should finally have unlocked access to the Fairy Village on top of Mt. Pachika. In the second area of the Fairy Village there is a Blue Fairy to the right of the screen next to the stairs. Talk to that fairy to get the scroll for the formation Square Dice.
Take that scroll back to the old man in Beginner's Cave to unlock the Square Dice formation and get the cheevo.
Sort of Missable since this is right at the very end of the game and it is possible to finish the last of the game without ever leaving Mt. Pachika and returning to the World Map. I don't know if the scroll itself is carried into NG+. It could possibly also be missed if you somehow got another ending after Quest 40.

Just FYI you have to equip curative items in weapon slots in order to use them in battle. Just stick one in a slot and then once you're in battle, you will be able to step over to the last action menu to find the items. I believe the Backpack item might allow you to bypass this, but I haven't tested.
All these cheevos are the same thing for different items.


You can get a Balm from the general item merchant right from the start of the game. Just equip one on any character and use it in combat to get the cheevo.
Not Missable.


You need to consume an Elixer for this cheevo. You might get one earlier on in the game from monster item drops or treasure chests, but later in the game after the requisite quests, they will be for sale for 10000 Gold from the general item merchant in town. Just equip one on any character and consume it in battle for the cheevo.
Not Missable.


You will get an item called Wagyu Beef as a reward for Quest 17. Equip it on any character and consume it in battle for the cheevo.
Probably Not Missable.


Same routine again. You get a Hamburger as a reward for Quest 34. Equip it on any character and consume it in battle for the cheevo.
Probably not Missable.

Just figured I'd put this here at the end in case anyone was interested....

I came across a little something in my searches for ways to make the grind in this game less strenuous...
RPG Maker MV Cheat Menu Plugin[github.com] by emerladCoder.
Since Cheat Engine doesn't work with RPG Maker games and this does, I figured I'd include a link here in case anyone wanted to get past all the tedium of battle and get to the naughties.


I didn't find this out until after finishing the game, but you can press A on the keyboard to bring up Fast Travel in town... Not sure about other places. All this time I thought the A on the screen was referring to the controller button.


Sophie is the best waifu.
Reason #1: She is the biggest. Both in terms of height and chest.
Reason #2: She looks like an Ara Ara Onee-chan type, but she is secretly an ultra-pervert beyond anything the other girls achieve. Even Nadia. Her solo events are priceless.
Reason #3: Her orgasm faces are comedy gold. She has the best expressions bar none.

Nadia is second. Partly because she is stacked, but also because she is a loyal and honest slut. She wants to be boned right from the beginning.

Iris is kinda crap because she has a random pauldron on one side for no reason, the smallest boobs and the most reluctant, combative attitude. Also pee scene. Gross. Seriously gross.

Sakura is worst... because of karaage. Filthy heretic. Also her dialogue annoys me.


Okay. All done now.
Enjoy Blursed Sophie: