| This article contains spoilers from the manga that has not been shown in the anime. Please continue reading at your own risks.|
- Related article: Young Nakano
5 years prior to the start of the story, Rena was seen defending the young Fuutarou Uesugi from getting into trouble with the police. Somewhere around that time, she would take a picture with him and Fuutarou would keep it in his student notebook. ("Together, Today with Tumult in Kyoto")
5 years later, Rena once again met up with Fuutarou Uesugi during his time of distress, wanting to provide him with some support. After exchanging her charm and taking away Fuutarou's image, she told Fuutarou that they will never meet each other for the third time and walks away before Fuutarou could reach her. ("Seven Goodbyes ④")
Rena then goes back on her promise during the Kyoto Trip arc, appearing next to Fuutarou after he talks to Yotsuba Nakano. Rena admits she used her mother's name, and wants him to guess her identity of the quintuplets. Tired and sick of the identity game, Fuutarou simply gets up and walks away, wishing to enjoy his school trip. ("Sisters’ War - Second Battle")
Rejected, Rena goes to a mall dressing room, removes her disguises and reveals herself to be Itsuki.
After the field trip had ended, Rena meets up with Fuutarou once again at the lake they first met. Fuutarou gives Rena a photo album of the quintuplets together at the trip. He expresses his deep gratitude toward Rena for having met him five years ago. After an indefinite amount of time, Rena is standing alone by the river's fence when Yotsuba emerges from the trees, calling her Itsuki. Rena, now Itsuki, apologizes for having acted on her own, but insists Yotsuba on telling Fuutarou the truth, that Yotsuba was the one who met Fuutarou as a child. ("Sisters’ War - Exhibition Match")
Ever since her introduction, various hints are given regarding Rena's identity.
- She has a charm similar to the charm Fuutarou bought five years ago.
- She gave Fuutarou her charm, which Fuutarou lost in the river, so one of the Nakano Quintuplets doesn't have the charm anymore (at the moment only Itsuki Nakano's one was shown before).
- Rena now keeps Fuutarou's photo of their younger selves. Itsuki dropped the same picture while she was putting away her items.
- Rena knows how Fuutarou used to look like when he was younger.
Starting at Third Year Saga, Negi Haruba starts giving a more detailed hint or revelation about Rena.
- Itsuki is revealed to own a box with Rena’s disguised costumes inside it.
- Itsuki explicitly shown to wear Rena's outfit in Chapter 79. She also tries to make Fuutarou acknowledges her identity as Rena during Kyoto Trip Arc.
- It is revealed that Yotsuba is the one that Fuutarou met when they were young
- ^ Volume 6 – There was a scene depicting a box of the disguised costumes