Honoka Shirahama, Kenichi Shirahama's younger sister, shares his short brown hair style minus the fringe, possesses brown eyes, and favors striped shirts, skirts, or her school uniform. Miu Fūrinji considers her very cute for her age, though she looks younger than she is.

Deeply concerned for her brother, she persistently follows him to the Ryōzanpaku dojo against his wishes, trying to persuade him to abandon his harsh training and come home. She harbors jealousy towards Miu Fūrinji, whom she nicknames "Big Chest" or "Titsy," convinced Miu is why Kenichi stays. This jealousy sometimes triggers emotional outbursts, including crying fits when Kenichi refuses her. She openly admires her father's dramatic actions concerning Kenichi.

On her second Ryōzanpaku visit, she properly makes tea, impressing Shigure Kōsaka and Apachai Hopachai. When Kenichi forbids her visits to see him, she continues coming under the pretext of visiting Shigure and Apachai, forming strong friendships with them. She regularly plays board games there, especially Othello, where she defeats masters like Apachai and Akisame Kōetsuji by narrow margins.

She befriends Natsu Tanimoto after he rescues her from thugs, ignoring his initial reluctance. Natsu sees her as a surrogate for his deceased sister, Kaede, while Honoka views him as another brother. Loki of Ragnarok later kidnaps her to target Kenichi; Hermit intervenes to save her from Number 20, an act leading to Hermit leaving Ragnarok. Despite this, Honoka persists in visiting Natsu's home.

Her Othello skills dominate Natsu, who frequently loses and fulfills her demands for dates, cooking, or massages. Her poor cooking and tendency to break items during cleaning inadvertently force Natsu to learn these skills himself. She attributes his improvement to her guidance, unaware his motivation is avoiding her substandard efforts.

Though lacking formal training, she knows basic martial arts techniques from observing her mother and Kenichi's training.