Koki Eto is a 19-year-old male born on May 22, standing approximately 175-177 cm tall with blonde hair, blue eyes, and blood type A. He leads the unit Growth at Tsukino Talent Production, central to the group's activities and dynamics. His strengths include a broad appreciation for music, proficiency in housework and academic studies, physical exercise, a fondness for animals, valuing friendships, and enjoying periods of inactivity. Throughout official media, Koki features extensively in unit-related events and promotions. He frequently appears in gasha banners, commemorative login screens, and event-specific cards like the "Tasogare ni Somaru" and "ALIVE FANTASY" series, depicted in both unidolized and idolized versions. His involvement extends to anniversary celebrations, including the 1st and 2nd Anniversary events, where Growth's cards and banner appearances showcase the unit's evolving themes and visual aesthetics. Musically, Growth performs the opening song "Mahou no Kizuna" for their dedicated story segments. Koki also engages in cross-unit collaborations, notably with Sora Ohara on the duet "Joushoukiryuu" for the ALIVE Neo X Lied series. Within this release, he participates in two drama tracks exploring themes of challenge and unexplored potential, reinforcing his narrative role within interconnected unit stories. His character representation expands across various merchandise lines and special in-universe events, such as the "Wanderful Smile" and "Starry sky collection" gashas.