Toradora!

Synopsis

Because the school's pool has finally opened for the summer, Minori, Ami, and Taiga buy swimsuits with Ryuuji. Ami and Minori easily pick out swimsuits while Taiga has trouble due to her small chest. Later, Ryuuji realizes Taiga's problem and decides to add padding to make her breasts look bigger and fill out her swimsuit. At the pool, people are throwing others into the pool, and Ami throws Taiga into the pool. It turns out Taiga cannot swim; when Ryuuji goes to save her, she tells him one of the pads came out. Ryuuji manages to work everything out and Taiga is saved. Back at the classroom, Ami and Taiga argue until Minori shows up, telling them to settle things with a sports contest. (Source: Wikipedia)