Kiriko is Kenji's older sister and Kanna's mother. For the vast majority of the manga, Kiriko is only seen in flashbacks, where she is shown to have a strong sense of justice and an interest in biology. She was also an important mother figure for Kenji during his youth, often taking him places or getting him presents and helping him out (like when he was hospitalized due to a motorcycle accident or when she got him an electric guitar).

Spoiler

Fukubei researched Kiriko's romance with Moroboshi and after he had him killed, began courting Kiriko in the same way as Moroboshi (i.e. using his words). His goal appeared to be to encourage her to fulfill her dream of studying microbiology and use her expertise to create the deadly virus. When Kiriko realized that Fukubei was creating a cult around himself, she gave the police everything she knew about him and left her child, Kanna with Kenji and their mother. Unfortunately, the detective she gave it to was Yama and he had already defected to friend at the time, so her evidence was destroyed. Kiriko then went to see Yamane and convinced him about Fukubei's true intentions. Upon realizing how deadly the new virus that Yamane made was, she decided to spend all her time and effort making a vaccine. Kiriko feels extremely guilty over her involvement in the creation of the virus, as such she has spend most of her time trying to out-maneuver Friend and create a vaccine that would be distributed to everyone. As a last gamble in Friend year 3, Kiriko exposes herself to the next generation of the virus to test out her own vaccine. Fortunately the vaccine works and Kiriko survives.

Spoiler

In 21st Century Boys, Kiriko seems to be working in some African country as a volunteer doctor. Kanna and Chouno come to see her, and daughter and mother finally reunite.