First Time With Someone Older

University student 'Han-san' sees 'Ji Eun-seong' who is working on a group assignment, and remembers seeing him having sex with a man in a bar bathroom the other day. San-eun approaches Eun-seong, who looks innocent, with a light heart... Why does it seem like he's just being swung around? It's all because it's the first time with someone older!