Yoshiki and Ayumi find the wire on one of the shower faucets (3rd from the right) and take it with them. It is used to pick a lock to classroom 4-A.
Episode #5; 『Shangri-La』
Sakutaro finds the wire on the shelf inside classroom 1-A. After finding the kite string he will use both to make a makeshift fishing line and try to fish out a shining object inside the hole in the first floor. After failing once he will try again and succeed, realizing that the shining object is a student ID that belongs to Mayu; a person he is searching for.