These 3 would most of the time stay after school to swim. You forget that they swam after school when you decide to study in the pool room.

The 3 come in

Inosuke: Who's ready to race he had a smirk (already in his swim shorts)

Zenitsu: Tanjiro volunteer 's (has swim shorts but still has a shirt.)

Tanjiro: Uh....sure inosuke! Taking off his shirt.