Koji Yatake, often called Take-chan by his friends, is a recurring character in the series. He is a classmate and close friend of Haruki Nakayama. Standing at a tall height, he works as a video editor for a small company, having majored in film at university. Yatake entered university a year later than his peers after spending that time retaking his entrance examination. He frequently combines his filmmaking skills with his interest in music, producing music videos for local acts. He also organized the venue and event for the first live performance of the band Given. Besides his video work, Yatake is a musician who plays bass guitar and provides vocals for his own band.

Yatake possesses a practical and observant personality. He demonstrates strong concern for the wellbeing of his friends, especially Haruki Nakayama. This protectiveness informs his interactions with Akihiko Kaji, towards whom he is particularly strict and watchful. He offers grounded advice and steady support, functioning largely as a confidant and facilitator for Haruki outside of the band's central tensions.

His most significant relationships are with Haruki Nakayama, his closest friend; Akihiko Kaji, whom he holds accountable due to his concern for Haruki; and Yayoi Uenoyama, Ritsuka's older sister, with whom he develops a stable romantic partnership. His personal development is primarily seen through his steady professional life as an editor and his maturing relationship with Yayoi. His notable abilities include professional-grade video editing and filmmaking, music composition and performance on bass guitar and vocals, and practical event planning.