Koichi Yamada (山田浩一) (Perman #5) is a minor character that only appeared in the Perman manga.
Koichi is a 2-year-old baby, and considered to be the youngest member of the Permen. In a volume, he saw Mitsuo Suwa as Perman. In order to protect Mitsuo's identity, Koichi was made a Perman. He wears a yellow helmet, pink cape, and a badge. Even though he speaks like a typical baby, he has a good deal of wisdom, and the ability to fight off criminals.
However, he only made appearances in the manga and 1960's anime adaptation, but after that, he never appeared again for an unknown reason.