So.
The point of this game is to find out the code from Saiko or from the blackboards in the classrooms.

You will spawn in a room that looks like this :

To the left and right there are 3 "containers" that can be opened and can contain the exit key:

When you leave the room or wait for Saiko to open the room for you (she is a bit clingy so it will be harder to lose her) go straight to the power room or collect pages scattered around school with the journal provided in the start office on normal or randomly generated in rooms in hard.

Do the puzzle by the electical box and now the game can truly begin.

Credits for the map : https://gtm.steamproxy.vip/id/Wolfkann
This is the layout of the school.

And here is a little bit more detailed variant of the school.

You need to find 4 keys but there is a catch .
On each corridor there will always be 2 doors that can be opened and 1 locked .
In the locked one there is a fragment of code (write it down somewhere when you find it)

The keys , classrooms and codes are randomly generated each time you start so you can't cheat.
When you are searching for keys remember that every corridor can hold 1 key
Example:

• Corridor D - 1 key
  
• Corridor C - 1 key
  
• Corridor B - 1 key
  
• Corridor A - 1 key

You can't find 2 keys on the same corridor so you know.

If you can't find a key it can spawn in the other rooms in the school , I will list them below

• PC Room
  
• Cafeteria
  
• Meeting Room
  
• Library
  
• Kitchen

In the game there is a journal that can be completed with pages found around the school and Saiko can or cannot (mood) tell you the code if you complete the journal .

On normal difficulty the journal is right on the table in the office and it looks like this:

On hard difficulty the journal is randomly spawned around the school
I don't know very much about the journal spawn locations in hard mode but I can provide a few locations where I found it :

Now the locations of the pages are again randomly generated hooray but not quite to be honest,
they can be found pretty easy. Here is a map of all possible spawn locations :

As you can see there is a pattern of some kind.
There are 4 locations that have 100% spawnrate

• Starting office
  
• Bathrooms by classroom D1
  
• Bathrooms by classroom B1
  
• Rooftop.

Oh and be careful to search each stall in the bathrooms AND both bathrooms because there are 2 man and female (duh).

After completing it hand it over to saiko (if she is the mood of talking) and she will tell you the code for the locker or kill you (woman moment).

In yangire mode there is no journal and Saiko is hostile 24/7 .
Pages there do something different .
Here is a guide to do exorcism on her with the pages.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2635747039

The things I explained are the basics off the game and where to starts .

If I find out more useful tips & tricks I will update this guide , until then good luck with best girl Saiko.