Explanation is needed at the end of Corpse Party - Tortured Souls OVA
Finally found a screenshot of the other student's ID.



Satoshi was using Yuuya's scrap, not his sister's; this resulted in his death on trying to return to his world. This is due to Yuuya not being a part of the ritual that Class 2-9 held, so his scrap could not bring Satoshi back.