Nanaka is a very beautiful young woman with long brown hair and reddish-brown eyes. Like Azusa Hamaoka, Nanaka has a very voluptuous figure and large breasts. Iori Kitahara mentions that she has a "phenomenal ass" like her sister Chisa Kotegawa. Nanaka is usually seen in casual clothes, like dresses.
Nanaka is a very sweet, nurturing and caring woman who takes the role of the mother hen within the group. She doesn't usually take part in the group's drinking and partying, preferring to observe. Like Chisa, Nanaka loves diving and is a diving instructor. She has a very severe sister complex when it comes to Chisa and the only time in which she sheds her sweet image is when it comes to Chisa, particularly in relation to Iori. Whenever Iori is mentioned to be Chisa's boyfriend, Nanaka becomes very hostile, frightening, and threatening, and would even resort to violence if necessary.
- Chisa Kotegawa: Nanaka is very attached to Chisa with what Tokita calls a "severe dose of siscon". Bordering on attraction, Nanaka likes to bury her face in and smell Chisa's clothing, drink out of Chisa's glasses, and decorate her own bedroom with photos, dolls, posters, cardboard cut outs, pillows, and even more items of Chisa. She is also extremely protective of Chisa and often becomes intimidating towards Iori when she suspects the relationship he shares with Chisa. Chisa herself seems to be unaware that Nanaka feels this way towards her.
- Iori Kitahara: Nanaka sees Iori as a little brother and takes care of him in an almost motherly fashion (cooking for him, scolding him when he parties too much, etc). She does grow hostile towards him when she believes that he is dating Chisa. However, Nanaka does genuinely like Iori (platonically) and even says that she would be okay if Iori married Chisa.
- Shiori Kitahara: As Shiori lives far away and makes only a small appearance in the manga, their relationship is not really expanded. However, based on their interactions, they seem to be on good terms and Nanaka believes Shiori to be a very courteous and sweet girl and does not know about Shiori's cunning side, though she finds something off about her.