SOS
https://bowlroll net/file/199701
As I understood the hint, the author requires:
"The full name of the girl who called the secret base as oyabin(オヤビン) + the class name of the childhood friend of the senior member of the club to which the girl belongs (from the first part of the password)."
So, I started to google the word oyabin and the name of the game. I only get two results, both lead to one girl(猫塚みけ). Obviously, this is the first part of the password.
Now the second part. 猫塚みけ belongs to a volleyball club. The senior member of this club is 梅園かな. Her childhood friend is 夢路まりあ. She belongs to class 2-B. In the formula from the author three passes(circles). Everything is perfect. I insert everything into the formula and ...
It didn't work.
I freaked out and just started bruteforcing all the classes. None of the classes worked (there are 9 of them). I even tried to remove the word クラス.
Then I paid attention to クラスの通称は. Google translates this phrase as the popular name \ common name \ nickname of the class. I think that there was a problem here,but no matter how I tried to find a popular name or nickname, I failed.
I'm at a dead end.