The Custodian's Key (用務員室の鍵 Yōmuinshitsu no Kagi ) is an item found in Corpse Party.
The custodian's key can be found in the fourth chapter. It is located inside classroom 5-A and jumps around the two sides of the room. It can be found by Satoshi and only acquired if Naomi is saved. It is also the factor as to why Satoshi tries to get Tohko Kirisaki to help him if Naomi is dead in the wrong ending.
It opens the red door to the custodian's closet.