Rykah's attacls are designed to steal and control the space around you. Keep your distance when she moves. Respect the space that she takes and when the amount of blades thin out, dash in and spam hit her.

A lot of Rykah's attacks will take up a large portion of the screen.
This can be very scary at first but is totally manageable. You need to play defense and keep some distance. Keep an eye out for the gaps in her attacks that will let you get close and land a few hits.
If you've ever played a souls game it's a similar to what you do in those games.

When to get cloase and attack Rykah isn't as obvious as it is for the other bosses.
She has no stun animation that can be triggered. Instead she just stands in place whenever she attacks and for a second or two after. Depending on the move their is usually enough time during or after an attack to land a few hits. Use your judgement to know which attacks its safe to go in during.

Get comfortable rolling while running and rolling multiple times in a row. Some of Rykah's attacks can only be avoided this way. Because you should be keeping some distance at the start of her attacks, you need to be able to get in quickly. This is where rolling while running is beneficial. Just be mindful that rolling while running will move you a different distance than normal rolls.

Disclaimer: I didn't check any files nor do I have any association with Carpetwurm. All my information I got just from playing the game for 6.9 hours the last 0.9 or so just being testing the Rykah fight and beating her on NG, NG+ and NG++ for fun. So take what I say with a grain of salt.

Rykah's fight is the most different out of any boss in Tailbound. Playing out closer to a bullet-hell than the typical 2D Zelda style bosses seen up until this point. Despite this, she's not too complicated.
The pattern I was able to notice was for when she attacks. It goes as follows:

• Move: Rykah will quickly fly off in a straight line to another nearby spot in the arena and stop there. During the animation when she's moving she is still vulnerable. Meaning that if you anticipate where she's going or if she happens to fly past you, you can land a hit as she flies by.
  
  
• Attack: After moving and stopping Rykah will attack one time. She never attacks consecutively in the same location. This is huge to know because it means trying to get as many hits in during an attack window has no downsides as the time it takes her to move provides ample opportunity get out of the way of her next attack.
  
  
• Repeat: Moving and Attacking immediately after are the only things Rykah does. Thus if she's moving, she's about to attack and if she's attacking she'll be moving shortly after the attack ends.

As for the different attacks she uses, here is a list below of what they do and how to counter them.

Attack: She fires a blast of red knives.
Counter: Just roll through the knives towards Rykah.


Attack: Rykah shoots a straight line of yellow blades.
Counter: Just sidestep the line or roll to the side.


Attack: Rykah shoots three straight lines of yellow blades.
Counter: Walk in the space between the lines or dash roll through the line towards Rykah.


Attack: Rykah shoots a straight line of white blades with two other lines orbiting it. The orbiting lines fire outwards after crossing once.
Counter: Just sidestep or roll the lines as they go outward.


Attack: Rykah creates four explosions of green knives which stop in place after overlapping the other explosion's knives and after a short pause rotate slightly and continue moving outward.
Counter: Roll to the center of an explosion when the blades first spawn. Then walk around the knives and be prepared to roll when they start moving again.


Attack: Two rings of purple and red shurikens expand from Rykah before collapsing back on her and continuing outward.
Counter: Roll in towards Rykah as the shurikens go out, roll back out as the shurikens collapse inward and finally roll back in as the shurikens fly outward again.


Attack: A rings of purple and red knives expands from Rykah before collapsing back on her and continuing outward.
Counter: Roll in towards Rykah as the blades go out, roll back out as the blades collapse inward and finally roll back in as the blades fly outward again.


Attack: Rykah fires a barrage white knives in while turning 180 degrees.
Counter: Roll diagonally towards Rykah through the blades.


Attack: Rykah fires several purple then yellow Knives while turning 720 degrees.
Counter: Roll diagonally towards Rykah through the blades and immediately roll through again.[/b]


Attack: Rykah fires a ton of multicolor knives in every direction. After doing this for a few seconds the knives will freeze in place (when they turn white) and then three bursts of purple knives will be fired along the frozen knives becoming unfrozen.
Counter: Get away from Rykah and walk around the knives, roll in once the knives stop and the bursts knife lines get fired out.


Attack: Rykah fires a thick blast of yellow knives in a pattern vaguely resembling a star.
Counter: Just roll through it towards Rykah.

Which play-through you decide to fight Rykah in won't affect how the fight goes all that much.
The NewGame and NewGame+ experiences are nearly identical. As long as you leveled Guts or Strenght at all during NG, then fighting her in NG+ shouldn't prove any more difficult than fighting her in NG.

Only meaningful difference being that NG+ allows for you to prepare items and grind to max level in advance if you really want to. Doubly so for NG++ or NG+3 as they allow you to bring extra Red Stones, trivializing the fight.

On NG at Guts Lv1 it takes Rykah 3 hits to kill you. While lots of her smaller moves can be avoided relatively easily. Due to her damage output it is important to keep your distance during her bigger AoE attacks which can hit you multiple times in short quickly if you're not careful.

For NewGame the only way to make the fight easier is to name yourself "Link" for the +2 Guts or "Ganon" for the +2 Strength stat boost.
Alternatively if you want to do the fight with all Lv1 stats naming yourself "Marisa", "Cirno" or "Reimu" makes reaching the fight more convenient on NG.

Allegedly NG+ has higher enemy damage, enemy health and attack speed.
Speaking from my personal experience it seems that these effects are negligible if you simply level up your Guts and Strength before starting the NG+ cycle. Meaning the fight difficulty hardly changes from NG, with one exception. NG+ Allows you to bring items into the fight from your NG cycle. Most items being so powerful that they drastically reduce the difficulty of the fight.
Recommended Items to bring are:

• The Red Stone: Definitive Best Item. Makes you invulnerable, letting you wail on her.
  
• Energy Drink: Heals you to full. Letting you make more mistakes and still win.
  
• Whetstone: If you can spare the inventory slot it'll allow you to end the fight faster.
  
• Padding: Worth considering if you keep getting hit and run out of energy drinks.

Check out this guide for where to obtain the Red Stone.

If you're fighting Rykah in NG++ I'm going to asume you don't intend on fighting fairly and are okay wasting time to have an easier time.

• Grind for Lv10 Guts and Lv10 Strength.
  
• Bring minimum of 2 Red Stones + energy drinks or whetstones.
  
• Profit

If you lose the fight while under these circumstances just close the guide because you're beyond my capability to help you. I'd suggest going for a walk.

Good luck with fighting the good fight out there.
Thank you for your time and please consider tossing a coin to your witcher because this took a while to make. This is my first time making a guide for a game or anything of the sort.
Any constructive criticism or feedback is appreciated. ^^