She is the biological mother of the Nakano Quintuplets who worked as a teacher. She was a teacher at a high school where she was well-loved and respected by her students. Shimoda was once her student. Rena is known to be a very serious, unsociable, strict, and stern woman, especially when it comes to teaching her students as she would often punish her students with iron-fist sanctions.

Spoiler

Rena was a single mother who raised five children. Before her remarriage with Maruo Nakano, she and the quintuplets were living in poverty like the Uesugi Family, where it is implied that the biological father of the quintuplets (Mudou) abandoned her and the children. She passed away five years prior to the start of the story on August 14 from an unknown terminal illness and her death was a shock to the quintuplets