<noinclude> <nowiki>*</nowiki> = optional row <PRE>

</PRE></noinclude>Kōsaka Mizuho (香坂 瑞穂) is a student at St. Lucia Academy who always carries a notebook. She currently only appears in the abandoned manga-only arc Utsutsukowashi-hen.

One day, she discovers a the body of a dead teacher floating in the swimming pool, and because she found him first, the other students suspect her. This is also the second time she discovered a corpse. Sister Maria tells Shion that she worries about Mizuho. A lot of students in her class claim that she is always alone and does not open up to anybody. The class representative Yukari bullies her. In the first chapter she steals her notebook only to have Shion take it back and return it to Mizuho.

Shion and Mizuho develop a friendship. The arc reveals that Shion knows her grandmother originally wanted to kill her when she was born. Mizuho reveals that her father was killed protecting her, and that was the first time she saw a corpse. Her mother sheltered her in St. Lucia. Shion gives her "Shion-san's special amulet", which is only an eraser, to apologize after she shouted at her. Shion claims that the amulet makes you feel better and can grant wishes when the carrier is in trouble. Mizuho also meets Ōtori Saki, a strange girl who talks to her about Mizuho's past and claims it was not the truth and that they are the same.

In the third chapter, Ōishi and Kumagai arrive at the school to investigate the death of a student one day after the teacher's death. Mizuho tells them that she saw a suspicious person at the place where the student died.