Yoichi Isagi (潔いさぎ世よ一いち Isagi Yoichi?) is the protagonist of the Blue Lock series.

Isagi is a second-year high school student, who previously played as a forward for the Ichinan High School football team. When he arrived at the Blue Lock facility, he became a member of Team Z for the First Selection. His main goal is to become the world's best striker. Isagi is easy-going and has a generally friendly, cheery personality, but his simple and innocent habits often get on the nerves of the people around him. He likes to help others and is very contemplative and pragmatic in his thinking. He tends to avoid any childish squabbles among other Blue Lock competitors and tries to be a peacekeeper between his friends and rivals. At the beginning of Blue Lock, Isagi is massively unsure of himself and his skill due to being the second lowest ranked player in Blue Lock initially and his conflicting ideas of football. As time goes on, Isagi develops a more assertive presence on and off the field, becoming the foundation for Team Z and garnering the respect of some of the best players in Blue Lock who mostly have heavily assertive or dominant personalities. As of Third Selection, Isagi has the confidence, charisma, and reputation to talk openly with Rin Itoshi, one of the most talented yet difficult people in the Blue Lock Project.