Gaku is a 12-year-old classmate and close friend of Naota's. He's the hyperactive type—a stark contrast to the bored attitudes of his friends—and usually hangs around Masashi. Fans often note that Gaku's most memorable trait is his constant use of "chu," a Japanese onomatopoeia that works as both a kissing sound and a mouse squeak. He leans on this pun relentlessly, especially when talking about Haruko. The English dub swaps "chu" for "smooch" to land the same joke for Western viewers. In the school play episode, he had a minor role as a mouse, which fit his whole thing perfectly. Beyond that, Gaku's basically a walking encyclopedia of weird rumors and urban legends—a lot of them pretty sexual in nature, which tracks for a hyperactive middle schooler trying to seem worldly.
Content compiled by AnimeList.moe from publicly available sources.
