Mr. Koizumi is the Katase High School Table Tennis club advisor. He recognizes Smile's gift and ability towards the sport and so vows to train him. When Mr. Koizumi was younger he was considered to be the best table tennis player in Japan, and was nicknamed 'Butterfly Joe' because of his extraordinary skills. Mr. Koizumi states that Smile reminds him of his younger self. He is also an English teacher.

Tsukimoto Makoto (nicknamed Smile) is a quiet high-schooler who's been friends with the loud and energetic Hoshino Yukata (nicknamed Peko). They're both in the table tennis club and are very good at it, though Smile's personality prevents him from winning against Peko. The club teacher however notices Smile's talent and tries to make him gain some sportive tenacity.<br>
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(Source: Anime News Network)

[Wiki (jp)](https://ja.wikipedia.org/wiki/屋良有作)

Makoto “Smile” Tsukimoto and his friend Yutaka “Peco” Hoshino have been playing table tennis since they were kids, but as they enter high school, they find that the game has changed. Seeing potential in them that they themselves don’t fully realize, the coach recruits them for the school team. Bringing out their best will mean challenging the top players from rival schools in the summer tournament, including an ace Chinese exchange student who almost made the Olympic team. With the pressure on, can Smile and Peco take the heat and make it into the finals?
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(Source: Viz Media)

Jou Koizumi