The item's location & The way to open the safe are shown in Cleaner's Memo / A Note from the Class President.
The player must unlock the safe in order gain access to the solvent.
The way to open the safe is different from the original and the remake.
- In the original ver, the player has to record the amounts of various balls ( baseballs, volleyballs, footballs, and basketballs ) that are left in classrooms 2-4, 2-5, 2-7, and 2-12.
- In the remake ver, there is a storage locker in the room has has various medels which is used to unlock the safe
- It is mistranslated as "Acid" in either Sonnori's leftover English draft or Unnamed's patch for White Day: A Labyrinth Named School (2001 / Original).
- In the original game, the player has to watch which sac Hee-jin goes into before dousing said sac. In the remake the player has to find infected plants located in the Main Building and douse them with the solvent.