Little President is at A Tender Age

Summary
There is a small party for Mimori's birthday in the Student Council's room. When Kiri asks Tsubaki what he wants for the drinks, Tsubaki tells him that he wants cola. Unfortunately, Kiri mistakes Chūma's shrinking drug for Cola and Tsubaki gets turned into a small version of himself just like Bossun, Himeko and Momoka have before. But, this time is a bit different from before, not only has his appearance regressed, but also his mind.

Because Kiri feels annoyed by the female Student Council members' treatment to little Tsubaki for being cute, he takes little Tsubaki to Sket Dan Clubroom. But, Bossun and Himeko treat little Tsubaki in the same manner. At the end, Tsubaki is bought back to normal but unconsciously still keeps calling Bossun "Onii-chan".