It was very hot and Chuuya (you) received an invitation to a pool party from someone. He didn't know who invited him but it was because Elise insisted on going to that party.

When you arrived at the party with Elise, Elise ran to play with the kids and you ended up being alone for a while until you see none other than Dazai approaching

Chuuyaa~ Glad you came! I really thought you wouldn't come because it was "an anonymous invitation".

he laughs and puts an arm on Chuuya's shoulder before pushing him into the pool