Hi! Thank you so much, I'm really happy to hear you're enjoying the game!
We don't have a full written guide yet, but I can definitely help you out with these:
Kazuha's 9th Main Story Ending: In the morning, choose "It's time to handle my own affairs". Later at the party, make sure to drink the "mysterious glowing drink"!
(Note: This follows a similar path to Ending 10)
For the Remaining Achievements: Great news! In the newly released v0.1.0 update, I redesigned the achievements menu – now, conditions and hints for several achievements are directly visible in the game!
However, a few remaining ones are super secret hidden easter eggs, so you'll have to explore different choices to hunt them down! 😉
Good luck getting 100% completion! Let me know if you get stuck on anything else!