Takuji Mamiya

Height: 164 cm

Yuki's classmate, Takuji, is the protagonist of "It's My Own Invention" chapter. He is a reclusive boy from an otaku subculture who's always stammering while speaking with others. Takuji rarely attends class as he spends most of his time secluded in his secret hideout that he had constructed under the school’s old drained swimming pool.

The original Mamiya Takuji died as a child during an incident in which he attempted to kill his younger sister, Hasaki, due to brainwashing by his mother. On the verge of death, Takuji (seemingly) uses the last of his remaining strength to take over the body of Mamiya Tomosane, his elder brother. Tomosane's personality would then disappear entirely for the next 6 years, only to resurface as Yuuki Tomosane after. At the end of the story in Jaberwocky II, Tomosane regains control over the body, erasing Mamiya Takuji forever.