According to Onigafuchi tradition, the Kimiyoshi family is always best among the three main families, and would automatically lead the village. However Kiichirō serves more as a figure head since the Sonozaki family's Sonozaki Oryō actually directs events in the village. Thus while Oryō really led the anti-dam movement, Kimiyoshi served as the Chairman of the Onigafuchi Defense Alliance.
In Hima tsubu shi-hen, even though almost the entire village knew that the young Akasaka Mamoru was a public security officer who came to Hinamizawa in June of 1978 ("Shōwa 53" in the traditional dating of the series) to investigate the kidnapping of Inukai Toshiki, Kiichirō kindly welcomed him as he entered the Defense Alliance's headqurters at the Furude Shrine.
In Wata naga shi-hen and Me aka shi-hen, Sonozaki Shion kidnaps and murders him. Disguised as her twin sister Mion, she attends the village board meeting at Furude Shrine to discuss the mysterious deaths of Tomitake Jirō and Takano Miyo. She declares that their deaths were the result of Oyashiro-sama's curse, because they entered the forbidden Saiguden during the Watanagashi Festival. From Shion's perspective, this appears to enrage all of the elders, including Kimiyoshi. She then tells them that both Maebara Keiichi and Sonozaki Shion also entered the Saiguden. After she mentions that Shion had already disappeared, Kiichirō coldly asks about Keiichi's current position without any sign of concern for Shion's safety.
Disturbed by Kimiyoshi's lack of concern for Shion, "Mion" lies to him that Oryō, whom she already murdered, wished to talk to him at Sonozaki Estate. There, Kimiyoshi expresses his concern for Shion by assuring "Mion" that he believes Shion should not be "Demoned Away" if she is sincerely sorry for her actions, and that he would personally vouch for her. However, he then added that Shion has a better chance of forgiveness than "Hōjō_Satoshi">that accursed Hōjō brat," since the Hōjō are doomed to be cursed for being pro-dam activists during the Dam Conflict.

Confused, "Mion" insists that the Sonozakis should have already forgiven Satoshi as part of the three fingernails Shion had ripped as penance for the three people who covered for her after she ran away from her
boarding school:
Kasai Tatsuyoshi,
Uncle Yoshirō, and Hōjō Satoshi.
Kimiyoshi explains that Shion's painful sacrifice paid for Kasai, Yoshirō, and herself. Enraged, "Mion" tases Kimiyoshil, locks him up in the Sonozaki underground bunker, and tortures him for information on Satoshi. Asked if he thought Satoshi was alive or dead, he answer.png.pngs that he finds it difficult to believe that Satoshi is still alive. She leaves him for two days, he dies, and she disposes of his body by throwing it into the well.
In the third anime season's Nekodamashi-hen, in one of Rika's many failed worlds he succumbs to Hinamizawa Syndrome and drowns Rika in the Onigafuchi Swamp.