Злополучная вечеринка

Banri discusses going as a couple to the beach over summer break with the upperclassmen of the festival club and is told he needs money first. When he tells Koko he wants to work, she rejects his idea, saying they would have less time together. However, behind Koko's back, Banri and Yanagisawa accept a job from Nana-senpai, and...?