| This article contains spoilers from the manga that has not been shown in the anime. Please continue reading at your own risks.|
Quintuplets Flashback Arc is covered in Volume 11.
- Start of the arc: A flashback about Rena Nakano and the Elementary School Kyoto Trip. (Chapter 87)
- End of the arc: Yotsuba's monologue and flashback. (Chapter 90)
Six years ago when the quintuplets were identical, one of them is about to change. An incident in Kyoto led her to meet Fuutarou and changed both of them, desiring to become 'necessary' to someone. Both parted ways and lived their lives until their eventual meeting 6 years later.
Time cuts back 6 years ago when the quintuplets were the same, the quintuplets are looking for a gift for their mother, the girls run into the soccer coach and are asked to play soccer, Yotsuba losing her wallet in the process, at the end of the day, the quintuplet's mother,Rena, arrives home only to be surprised by her daughters giving her a flower bouquet and congratulating her for getting better.
The quintuplets go on a trip to Kyoto, there Yotsuba saves a young Fuutarou from the police and spends the whole day with him, time goes by and Rena, their mother, dies because of her illness, now alone, the quintuplets remain in Maruo's care.
As time goes by the Nakano Quintuplets become first year high schoolers, Yotsuba gets expelled for failing her second make-up exam, her sisters decide to lie to the school higher-ups and end up getting expelled as well. Now at Asahiyama High School, Yotsuba reunites with a now studyholic Fuutarou, time cuts back to present times and Yotsuba is playing on the swings, revealing she had feelings for Fuutarou all this time.