Remorseful murderer Mizuho Ninomiya
Mizuho Ninomiya (Mika Kanai) is a remorseful villainess from St.Valentine Murder Case. She was one of the guests at the Snow Candle Lodge and the younger sister of Shizuka Kisaragi.
Mizuho's backstory revealed that she and Shizuka lost their parents at young age in an accident. Both sisters became good friend with Kaoru Shimazaki whose parents owned the orphanage that took them in. Mizuho and Shizuka were eventually adopted by a different family, much to Mizuho's displeasure, but calmed her down and promised her that they will live together once they finished highschool and she'll celebrate Mizuho's birthday, which's also Valentine Day, with her every years. Though they were apart, Mizuho, Shizuka, and Kaoru kept in touch with each other as Mizuho waited for a day to reunite with her sister. However, on the year of promise, Mizuho recieved a phone call from Kaoru who informed that Shizuka had committed suicide, with the last word the latter heard from Shizuka was "Kyogoku". Fueled with sadness and anger, Mizuho tracked down the information about "Kyogoku" and found out that it referred to Yusuka Kyogoku, Shizuka's boyfriend and a former heir to the infamous Kyogoku Hospital. She began researching about the man and found out that not only he was a notorious playboy, but he was also a doctor who had once refused to examine Shizuka's illness in the past, resulting in it being untreatable and that Shizuka would only live for a few more years at most. Believing that Yusuke was only playing with Shizuka's feeling and dating her because she didn't have much time left, Mizuho plotted to murder Yusuke to avenge her sister. At this time, Mizuho also discovered that Takuya Kyogoku, who's Yusuke younger brother, had randsacked Shizuka's room the same day she committed suicide and called Tsukasa Aoyama, Shizuka's employer at Snow Candle Lodge, about the suicide, and decided to get the answer out of him as well.