Shin Yūki is a second-year student in Class B at Adalbert Senior High School and serves as the vice-captain of its futsal club. He has wavy violet hair and blue eyes.

His father works as a diplomat, a profession that led to Shin spending frequent holidays in the Netherlands and Switzerland. He possesses a gentle and kind nature, often showing concern for his teammates. This kindness brings him into conflict with the club's captain, Louis Kashiragi, whose unreasonable practice regimens Shin finds frustrating. He holds a strong dislike for lies and vanity.

Shin shares a long-standing childhood friendship with Louis Kashiragi. Louis, who moved to Japan at a young age, considered Shin his only friend and now views him as a right-hand figure and family member. Within the team, Shin handles practical duties such as preparing brewed tea for club meetings, a skill he learned from an elderly person. He was also responsible for recruiting Tomoe Futaba to the club after recognizing his talent.

His personal hobbies include assembling jigsaw puzzles and visiting aquariums. He is skilled at billiards and can tie a knot in a cherry stem with his tongue, a trick taught to him by his female cousins. He has an affinity for the ocean. His favorite food is omurice, but he dislikes super spicy foods. Academically, he struggles with biology, especially the dissection component.

His star sign is Scorpio and his blood type is O.