Kie Tsutsui is married to Mitsuru Tsutsui and is the mother of two sons, Hikari Tsutsui and Kaoru Tsutsui. She appears as a middle-aged woman with puffy dark blue hair and blue eyes. A flashback in Season 2 Episode 3 depicts her youth, showing her as a beautiful woman with shoulder-length hair styled to fall on either side of her face.

Her role centers on her family relationships. She is Hikari's mother and Kaoru Tsutsui's mother. Kaoru maintains a distant relationship with his older brother Hikari. Her interactions with her sons are not detailed in the available sources.

Her given name "Kie" uses the kanji for "chronicle" (紀) and "bay, inlet" (江). Her surname "Tsutsui" combines the kanji for "cylinder, pipe, tube" (筒) and "well, mine shaft, pit" (井). She works as a housewife (shufu).

The available information details no significant character development, personality traits, direct involvement in plot events across official media, or background story beyond her immediate family connections.