Miō doesn't seem to care about Kaya much even though they are sisters.
He is the love interest of Miō. Back in the day when they were at the Nanohana house, she called him "Kazu-nii" and still does in the present. However, she despises the Hayashizaki family, because she thinks they "stole" Kazuki from her. At first, she acts like a tsundere, but later opens up to him and tells that she was very sad when Kazuki forgot about the times with her in the Nanohana house. Miō becomes very jealous when other girls try to get close to Kazuki.
This has later been massively toned down as she stated to Kazuki that she is fine with him dating other girls as long as he makes time for her and does not show the classic 'tsundere' behavior common in other shows of similar nature.
Mio's adoptive father. Even though he can be a little overprotective towards her they have a loving father-daughter relationship.