Matryoshka of Russia

Byodoin reveals this technqiue while trying to pick up a mafia lady during the Pick-Up Contest. Byodoin serves, and his tennis ball opens. Inside comes out a smaller tennis ball, still travelling forwards and then another smaller tennis ball pops out (Kirihara makes a reference to matryoshka dolls here). This process repeats 7 times.

In the pick up contest the final tiny ball flies into a mafia member's gun barrel which causes it to explode when attempted to be fired.