Haru Kaidō is the eldest son of the Kaidō family and one of the main characters in the second season of the series. He is a young man of twenty-four years old who has a distinctive appearance, characterized by his platinum blonde hair and light green eyes. This exotic look is a result of his heritage, as he grew up in Canada until the age of eight and has one-quarter foreign blood. His mother is Haruko D. Dieckmann, and his half-brothers, Aki and Shima, are his father's children from a different mother.

The background leading to the events of the second season is marked by tragedy. After being tricked into returning to Canada by his mother, Haru met and grew close to a young, antisocial orphan named Ren, whom his mother had adopted. He promised that they would live together in Japan. However, on his way back to the airport, a car accident killed his father and stepmother and left Haru in a coma. The accident also caused him to lose all memories of the summer he spent with Ren. Years later, after recovering his memories, Haru now lives in Tokyo with Ren and his half-brothers, running a café connected to their home called White Fang.

In terms of personality, Haru is portrayed as a good-natured, friendly, and caring individual who is naturally good at taking care of others. He is often described as being slow to understand other people's intentions and emotions. A defining characteristic is his strong sense of responsibility as the oldest brother; he feels compelled to protect and provide for his three younger siblings. This sense of duty is deep-seated, as a past trauma still haunts him: he continues to blame himself for the car accident that killed his parents. His motivation in the second season is to maintain a stable life for his family while struggling with the complex dynamics of his relationship with Ren.

The core of the story revolves around Haru's key relationship with Ren, his adoptive younger brother who is now a teenager. The central conflict of the second season stems from Haru's contradictory behavior. He frequently acts as a father figure or guardian, providing Ren with everything he needs and dismissing his advances. Yet, he is also physically affectionate with Ren, often kissing him, which sends mixed signals and creates significant tension between them. Haru is uncomfortable with Ren's desire to be seen as a romantic equal, citing the age gap and Ren's youth as the primary reason to hold back, even as he struggles with his own feelings.

Throughout the second season, Haru displays jealousy when other people show interest in Ren and is protective of him. His relationships with his other brothers, the twins Aki and Shima, are more stable, as he worked as a host in the past to pay for their college tuition and continues to care for them. His biological mother, Haruko, remains a distant but influential figure, and a cousin named Natsuo Shiba also appears, whose history with Haru introduces new complications.

Haru's development in the second season is largely about his internal struggle. He is an adult who is emotionally immature and often the source of the conflict in his relationship with Ren, as he has not learned how to properly communicate his feelings. He attempts to navigate the blurred lines between being a guardian and a lover, but frequently relapses into treating Ren like a child. His notable abilities are not combat or special skills but his capacity for hard work as a café owner and his innate talent for taking care of people, even if that instinct sometimes manifests as being overbearing.