第4話: 両親から卒業祝いに温泉旅館の招待券をもらったケイタは、女の子たちと温泉旅行へ向かう。

4

The sibling's parents give Keita tickets to a hot spring resort as a graduation gift and suggest that he take the girls along on the trip. The siblings go to the hot spring resort, end up visiting an erotic museum, and find themselves in some compromising situations involving Ako's unintentional purchase of alcohol. (Source: Wikipedia)