Kine Ryutaro is a character from the baseball story H2: Kimi to Itahibi, serving as a key member of the Senkawa High School baseball team where he plays center field and acts as the second pitcher. A self-proclaimed genius, he is highly athletic with quick feet and a strong throwing arm, though his personality is often described as cheeky, smug, and selfish. His true nature is frequently insidious and he is known for holding onto the weaknesses of others, yet this arrogant exterior masks a character who works hard and is more capable than he often lets on.

Kine's background in baseball is significant, as he was once the ace pitcher for the Hakusan Angels little league team. However, his intense and burning rivalry with the prodigy Tachibana Hideo led to him being kicked off the team, after which he quit the sport entirely and turned to soccer. Upon entering Senkawa High School, he became a promising player for the soccer club. His motivations shift when he becomes infatuated with Koga Haruka, the manager of the school's struggling baseball circle. In an attempt to disgrace the baseball club and force Haruka to become the soccer club's manager, he arranges a match between the two teams. This plan backfires when he finds himself hooked again by the presence of Hideo during a subsequent match, reigniting his passion for baseball and leading him to officially join the baseball team.

In his role on the team, Kine acts as the leadoff batter and a table setter, and his combination with the second batter, Yanagi, is highly effective at getting on base. He is a stable defender in center field, a position where his talent is said to rival that of Hiro. As a pitcher, he throws a sharp twelve-to-six curveball with good control, making him a solid second option behind the ace. One of his most notable quirks is that he is a left-handed hitter as a tribute to his favorite player, Masayuki Kakefu, though he will occasionally switch to hit right-handed against left-handed pitchers. His early relationship with Haruka is driven by his superficial crush, but he eventually abandons this attachment and forms a genuine couple with Miho Osanai, a girl who initially teamed up with him to scheme against Hideo. Throughout the story, Kine transforms from a seemingly one-dimensional antagonist and comedic flirt into a dedicated and reliable player whose hard work and true potential come to the forefront.