Haru Asai is a 35-year-old former professional soccer player thrust into the Eternal Boys idol group. After high school, he pursued soccer, where his goal-scoring prowess overshadowed his technical skills. An injury triggered his career's decline, seeing him overtaken by peers and juniors. At 34, formal notification of his removal from the team roster ended his athletic career.

He possesses a fierce competitive streak, strongly disliking defeat and becoming easily carried away. His personal life includes a divorce and fatherhood, making him the group's sole parent. Standing 170 cm tall with blood type B, his surname "Asai" (浅井) combines "shallow" and "well", while his given name "Haru" (悠) signifies "permanence".