Honoka Shirahama (白浜ほのか) is Kenichi's younger sister, who cares for her brother greatly, often competing with Miu for his attention. The second time she visits the Ryōzanpaku dojo, she shows Shigure and Apachai how to properly make tea, which impresses them. Honoka soon becomes good friends with the two masters and consequently visits the dojo regularly to play with them.
Honoka has a similar hairstyle to that of her brother Kenichi, being short brown hair except she has no fringe in the front. She typically wears striped shirts or her school uniform or a dress. Miu describes her as being very cute for her age.
Honoka is friendly and kind towards others. She loves her big brother very much and enjoys watching his training and is worried over how hard he has it at Ryozanpaku. She enjoys hanging around Natsu and thinks of him as another big brother (as Natsu thinks of her as his deceased little sister).
She has a bit of a mischievous side, often following her brother to the dojo that he trains at, despite him telling her not to, and trying to make him come home. She even broke into his room and tends to annoy him because she likes being with him. She seems to be a bit jealous Miu, who she calls "Big Boobs" due to her figure, believing her to be the only reason Kenichi stays at the dojo, which isn't completely true as he just wants to become stronger to protect his loved ones. She tends to lose her temper when upset and leaves in crying fits such as when Kenichi refused to go home. She tends to be impressed by her father when he tries to do something overdramatic, often believing it to be the right thing to do, especially with anything pertaning to Kenichi.
Honoka enjoys hanging around Shigure and Apachai, whom she plays board games with. She also often teaches them minor things they are unaware how to do such as how to make tea. She knows some level of martial art moves due to her watching her brother train and having her mother teach her some techniques.
Honoka's first major appearance was when she followed Kenichi to Ryozanpaku to find out what he was up to. Upon her arrival she discovers the cruel training her brother goes through and deduces that he goes through it all for the sake of Miu, whom she thinks is evil and refers to as "Big Boobs. During her second visit to Ryozanpaku, Honoka shows Shigure and Apachai how to properly make tea, which impresses them. Kenichi orders Honoka not to ever come to Ryozanpaku to see him again, to which she agrees. Since then she has constantly returned to Ryozanpaku under the pretense of seeing Shigure and Apachai, stating that Kenichi said "She couldn't return to Ryozanpaku to see Kenichi". Honoka soon becomes good friends with Shigure and Apachai and consequently visits the dojo regularly to play with them.
She later befriends Natsu Tanimoto after he saved her from some thugs and follows him to his home, despite his attempts to chase her out. When Loki appears, she demands to know why Tanimoto wants to hurt her brother, believing that they could become friends. Both fists of Ragnarok are shocked to learn that Honoka is Kenichi's little sister and Loki decides to kidnap her, despite Hermit's protests. The resultant battles end ironically, with Hermit saving her from Number 20 and leaving Ragnarok.
After this incident, Honoka still continues to visit Natsu's house whenever she pleases. Their relationship can be tributed to the fact that Natsu sees a resemblance in her to his deceased sister Kaede, and Honoka not having her brother to spend time with because of his training. While Natsu protests to her visits, he has become fond of her.
Honoka is also extremely talented in the game Othello, which she often plays with Apachai and Tanimoto. These repeated games produced admirable results for Apachai, who could only be beaten in the game by Honoka and Akisame, and even then, only barely. Kenichi has also hinted at the possibility of Honoka being better than Akisame in the game. Tanimoto is often forced to do anything she asks after he loses, which happens more frequently than not much to his embarrasment, though he refuses to quit challenging her due to his refusal to accept defeat. This often results in Honoka forcing Tanimoto to take her on dates or letting her cook for him, or even giving her a shoulder massage.
As a result of Honoka breaking things while cleaning and not having much skill in cooking, Natsu has had to learn how to cook, quite well in fact, and clean. Honoka believes, and has told Niijima, that it's because of her guidance, while in reality she does not realize that Natsu has learned how to cook and clean to avoid her breaking things and having to eat her bad cooking.