This Prank Will Leave You Breathless! (Blue Archive) (Patreon)

Mutsuki, who loves to do pranks, told Sensei about a buried treasure... But it wasn't a prank, the treasure is there! Turns out the prank was the "equipment" she brought for the salvaging operation was a mere small air tank, and even though both of them have to spend quite some time underwater, she refuses to share it with Sensei... 

Included: bonus pic and the message log between the two ;^)