Kiku Takane is both sister and coach to Ryuji Takane after their father Gou Takane's death, assuming significant responsibility young. She and Ryuji fled their abusive stepfather Tomizo, who physically mistreated their mother Chiyo and the siblings; their departure featured a confrontation at the train station where Chiyo pleaded unsuccessfully for them to stay, though Kiku promised they would return after achieving boxing success.

In Tokyo, her natural strategic aptitude for boxing—inherited from their father—surfaced early. She recognized Ryuji's potential despite his reluctance, employing rigorous training to develop his skills while navigating their hardships. Her analytical abilities showed during Ryuji's first fight with Jun Kenzaki, where she stepped in as his second, using psychological tactics to undermine Kenzaki's confidence mid-match. Her coaching later expanded to strategizing for Team Japan during international tournaments like the Jr. World Championship matches against Italy, France, Germany, and Greece.

Her relationship with Jun Kenzaki shifted from rivalry to mutual respect and eventual marriage. They had a son, Rindo Kenzaki, protagonist of the sequel series. Tragically, Kiku and Jun died when Rindo was young, leading to Rindo being raised by their teammate Ishimatsu Katori. Kiku faced direct peril when the Shadow Clan captured her to provoke Team Japan, resulting in Ryuji's solo rescue mission.

Kiku remained emotionally anchored by her commitment to reuniting with Chiyo, frequently writing letters to her mother throughout their journey. This goal fueled her persistence through setbacks. Her resolve faced its ultimate test during Ryuji and Kenzaki's brutal final professional bout, where Ryuji died shortly after victory. Kiku awaited the outcome at their wedding ceremony, wearing Chiyo's dress, and received Ryuji's body with a proud smile alongside Kenzaki.