Gaku Manabe, age 12, is another one of Naota's classmates and close friends who is obsessed with kissing and other things of sexual nature. In Episode 3:"Marquis de Carabas", 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 appears in the epilouge next to Masahi in their new school uniforms for Junior High.