Sonoko Sakanoue

She has purple hair and purplish-red eyes. She appears in the 10th week and is Ryoba's 10th thorn in her side. She's a reporter's partner. She was once a student here but returned, claiming to be studying to graduate. In reality, she's secretly observing Ryoba to determine if she's a murderer. She approaches Ryoba's senior to manipulate Ryoba into being jealous, thus investigating whether Ryoba is truly a murderer. She doesn't have romantic feelings for Ryoba's senior. She has a cold and serious personality, is skilled in mathematics and investigation, and is a moderately good student. However, she doesn't dare reveal that Ryoba is a murderer because she fears Ryoba's revenge. She has her reporter partner speak for her instead, but Ryoba isn't imprisoned due to insufficient evidence. She never speaks to Ryoba again. She is bisexual but doesn't trust easily, always checking lunchboxes before giving them to others or eating them herself (in 1980, at a Japanese school).