Sharp Rock is a minor item introduced in Corpse Party: Blood Drive only shown once in a cut-scene in the abandoned bomb shelter.
Corpse Party: Blood Drive Edit
CHAPTER 09 『 Imperator 』 Edit
After Naomi Nakashima realizes the key to taking down Sachi Shinozaki lies in her cursed eye, she decides to make a choice. She grabs the Sharp Rock and braces herself, before plunging it into her eye, hurting Sachi as well.