Shinobu Kirishima is the head maid of the Hōjō family, fiercely dedicated to protecting and overseeing Reika Hōjō. Her distinctive short white hair and red eyes accompany a traditional frilled maid uniform, and she always carries a wakizashi sword ready for her protective duties. She maintains a strictly formal and respectful demeanor exclusively toward Reika, consistently using Japanese honorifics. Conversely, she exhibits open hostility and blunt speech toward Shungo Ninomiya, whom she considers unworthy of Reika. This animosity manifests in repeated attempts to execute him, though Shungo often thwarts these efforts with defensive skills like bare-handed blade blocks. Shinobu's antagonism stems from her belief that Shungo causes Reika distress and reflects her general disdain for men interfering in Reika's affairs.

Classified as an "Action Girl" within the series' combat dynamics, she occasionally collaborates with Mitsuru Hosaka, Reika's other primary bodyguard. Her role extends beyond the Hōjō household after a vacation on a private island, leading her to join the main cast and integrate into daily life at Shungo's residence. Her narrative function centers on providing comedic antagonism through relentless assassination attempts against Shungo and demonstrating unwavering loyalty to Reika.