Yukako Yamagishi (山岸 由花子 Yamagashi Yukako?) is a side character and ally featured in Diamond Is Unbreakable. She is featured centrally in the Yukako Yamagishi Falls in Love and the Yukako Yamagishi Dreams of Cinderella story arcs.
Besotted with Koichi Hirose, Yukako first tries to kidnap Koichi before she is neutralized and appears later as an ally among the group agreeing to watch for the killer terrorizing Morioh. She eventually begins a relationship with Koichi.