Huh, aren't you ○○-kun from middle school? What were you doing drowning in a shallow public pool?

Eh!? You're in high school and you still can't swim so you're practicing!?

...Since I'm here, want me to teach you? I was the swim club captain in middle school after all.

In middle school

You got supplementary lessons? What kind of loser doesn't know how to swim!? Artist probably meant 補習, not 補修

You know how to control your breathing?

You turn your face towards the arm you're stroking with... Eh? ...It's got nothing to do with armpits.