TV-Series
Description
Nanaka Kotegawa works as a diving instructor at her family's Grand Blue diving shop on the Izu Peninsula. She is the daughter of shop owner Toshio Kotegawa and the older sister to Chisa Kotegawa. Nanaka possesses long brown hair, reddish-brown eyes, and a notably voluptuous figure that often draws attention within her social circle.

Her demeanor is typically gentle, caring, and nurturing, frequently taking on a maternal role, especially towards her cousin Iori Kitahara. She demonstrates this care through actions like preparing meals for him and expressing genuine concern for his welfare. However, Nanaka harbors an intense, obsessive affection for her younger sister Chisa, described as a severe sister complex. This manifests in behaviors such as smelling Chisa's clothing, drinking from her glass, and extensively decorating her personal space with Chisa's photos and memorabilia. Suggestions or rumors of a romantic relationship between Chisa and Iori trigger a dramatic shift in Nanaka's demeanor, revealing hostile and threatening protective instincts that can escalate to physical aggression. Despite this possessiveness, she claims she would accept Iori marrying Chisa if it guaranteed Chisa's happiness.

Nanaka maintains a reserved distance from the Peek a Boo diving club's frequent drinking and nudity, preferring to observe rather than participate. Her presence alone influences the club members to moderate their behavior. She shares a close friendship with Azusa Hamaoka, often confiding in her, particularly about worries regarding Iori being negatively influenced by the club. Nanaka was a member of Peek a Boo during her university years alongside Azusa, Shinji Tokita, and Ryujiro Kotobuki. Their past includes implied unresolved romantic entanglements that led to their current platonic dynamic.

She perceives Shiori Kitahara, Iori's sister, as courteous and sweet, remaining unaware of Shiori's manipulative tendencies. Her given name, Nanaka, combines meanings for "apple tree" and "flower," while her surname Kotegawa translates to elements meaning "old hand" and "river." Across official media, she is consistently portrayed clothed, avoiding the club's characteristic nudity. Her background story receives minimal explicit development in adaptations, with her core traits and relationships remaining stable.