Back in middle school, they were in the same class in their second year and she'd been scouted by a family member to be a grauvre idol and was asking their homeroom teacher for advice. The teacher was against it from the start, basically killing her confidence. Forgot what Saigi was doing, but he ends up going to where they are and basically tells Nui not to listen to the teacher because the teacher just wanted to avoid trouble and then called her cute. This is when she falls for him even though he hadn't even spoken to her before then.