Isaki Kudo serves as the paternal aunt and primary caregiver to Chika Kudo following the death of his grandfather, Gen Kudo. She houses Chika in her high-rise apartment, signaling financial stability likely from a high-paying job. Her personality is strong-willed, independent, and blunt, marked by a quick temper and a no-nonsense attitude. She asserts authority over Chika and is not easily defied. Isaki expresses care through practical actions and direct advice rather than overt affection, offering solid guidance to Chika and members of the Tokise High School Koto Club. She exhibits habits typical of an "older sister" archetype, such as walking around her home minimally clothed and casually delegating tasks to Chika. Her relationship with Chika blends sternness with familial duty. She provides him a small, expandable sleeping space in her apartment, reflecting pragmatic support. Though she frequently scolds or physically disciplines him for minor infractions, this underscores their familiar bond rather than hostility. Isaki actively encourages a romantic connection between Chika and Satowa Hozuki, often orchestrating scenarios to bring them closer. Isaki shares a friendship with Suzuka Takinami, a math teacher at Tokise High School, stemming from Takinami assisting her during a cooking training camp. They are also alumni from the same high school, with Isaki being Takinami's underclassman (kouhai). Her background includes learning koto from her father, Gen, though she does not actively play the instrument in the series. Personal interests involve indulging in sake and spending holidays either sleeping extensively or shopping. Her name "Isaki" combines "clothing, garment" (衣) for "I" and "blossom" (咲) for "saki," while her surname "Kudo" means "long time" (久) and "distant, far" (遠).