The student council secretary in Oogai First Public Middle School. She's Mana's childhood friend. She was always protected by her back then, which makes Rikka always believe in Mana, but Rikka always protected Mana when she was a trouble maker. She is also one of the ten best students in national mock exams. She introduces herself as "The light of intellect! Cure Diamond!!" (英知の光！キュアダイヤモンド！！ Eichi no hikari! Kyua Daiyamondo!!)