Gaku Manabe, age 12, is another one of Naota's classmates and close friends who is obsessed with kissing and other things of the sexual nature. In episode 3, he plays the part of a mouse in the school play. Gaku also uses the word "chu" constantly, especially when referring to Haruko Haruhara. This is a pun in Japanese, because "chu" is the Japanese onomatopoeia for both kissing and the sound a mouse makes. In the English version, "chu" is replaced with "smooch" to make more sense to English speaking audiences.
He's somewhat hyper compared to the bored composure of his friends and is usually seen with Masashi Masamune. He is an encyclopedia of bizarre rumors and legends, many of which are sexual in nature. He consistently refers to Mamimi as Naota's "wife". He, along with Masashi and Ninamori work as a delivery service for Masashi's family in their truck in episode 5. The truck is later destroyed in episode 6 as he and Masashi run from the berserk Terminal Core.
He watches the events of the episode happen, as well as appearing in the epilogue next to Masashi in their new school uniforms for Junior High.
Gaku debuts in episode 1 where he makes a comment about "Naota's wife," Mamimi.
Gaku is a talkative and expressive person who finds humor in theorizing about the unknown. He answers almost all questions others can not with some sort of legend tied to the odd goings-on of Mabase. When it comes to women and relationships, he somewhat represents the "immaturity" that Naota sees in kids his age. Quandaries relating to the women around Naota will undoubtedly lead to a sexual tangent and/or kissing noises from Gaku. He can also be seen as a mouthpiece for Ninamori and Masashi, who are relatively quiet but just as curious. Otherwise, he shares the bored, hum-drum demeanor of his friends.