After seeing his wife off on a trip, Masahiro was busy with the housework. But his sister-in-law offered him a helping hand. "I'll do everything for her, so please let me stay over for one night." He was left alone with his sister-in-law, Yuko, who suddenly showed up. He couldn't help but swallow his saliva at her unconcealable seductive charm and beautiful face. This wasn't going to be good. He ran into the bathroom to avoid crossing the line somehow, but...