Usui

A staff member of the island's school. He is in charge of maintenance of the buildings.
He died from falling from the campus roof due to a broken ladder.
It was Shuichiro who broke the ladder; he cut the nails from second footboard from the ground in order to injure Usui. Unfortunately, the ladder was flipped over, and that resulted in the accident.
Kuwadate was the one who flipped the ladder. He wanted to kill him out of jealousy and hatred.