Here is the Juken Jigoku all achievements guide. hope it helps you. if you have any problem. let me know.
(The fastest way to get this is to intereact with your friends until they repeat themselves at the start and at the school gates, every vending machine, every mailbox, and as many items on the table as you can.)
3rd floor locked door that cannot be opened with a key, that has this poster next to it.
spam it till the “door is locked” message pops up a few times and it should open.
make sure you check the beginning of the game!!
go to the very left street and folow all the way until you get to this dark area (behind them)
it will be in the right corner
go down the middle street and look for this little alley way. go down it until you get to the vending machines
it will be next to the trash can on the left side of the vending machines
#3 the school grounds
go west all the way till you are near the corner with the manhole. on the right of the trashcan near the doors it will be on the ground
it will be in the classroom right after class 1-3 in one of the corners
it will be on the second floor next to the locker on the outside of the classes directly behind the second door of class 2-3 (depending on which way you came it could be the first door)
in class 3-3 next to the teachers podium
in class 3-2 in the corner
The Last One
in class 4-3 on top of the shelves here!