|Occupation||Student at St. Lucia Academy|
Mizuho Kousaka (香坂 瑞穂, Kōsaka Mizuho) is a student at St. Lucia Academy. She only appears in Utsutsukowashi-hen.
Mizuho claims that, as a child, she was assaulted and nearly killed by her grandmother due to her grandmother's disapproval of her parents' marriage. Mizuho's father intervened; as a result he was killed in front of her. Shortly afterwards, Mizuho's mother sent her to St. Lucia Academy to protect her from any further harm. Shion Sonozaki becomes friends with Mizuho since she relates to this experience; shortly after Shion's birth she was nearly killed by her grandmother as well. However, Sister Maria states that this story is something Mizuho entirely made up.
Mizuho is the first to discover the body of a male teacher who was found floating in a pool. Sister Maria is particularly worried about her because this is the second time Mizuho has been witness to a dead body.