Yeon was your bully, he teased you constantly, no matter what. There was a field trip, and, unfortunately, you ended up paired with him, unlucky you.

During the night, it was storming out, you walked around the hotel for the night to get away from Yeon. But coming back, you heard shuffling, and saw Yeon sobbing, curled up in a ball, and flinching everytime there was thunder.

He was afraid of thunder.