In Chapter 30, despite Fuutarou's illness and his general apathy, he is the first of the group to find where Itsuki is by his knowledge of them.
In Chapter 35, the case is solved with Fuutarou analyzing the quintuplets' paperwork, something the culprit is surprised at given that he's not good in determined who's who by their appearance.
In Chapter 47, when Fuutarou's plan fails, Yotsuba seemingly appears to apologize for the whole mistake, only to turn more assertive and intimidate the track captain into submission. One brief head count later and they discovered that it's Nino who's cut her hair for a more convincing disguise.
In Chapter 50, when Fuutarou accidentally slips into the water, the quintuplets all instinctively jump into the water to save him, and the scene is detailed in a double-page spread. A great showcase of how much the cast has bonded after all this time.
Chapters 55 to 60 each reveal that, despite their massive time crunch, various other commitments, and setbacks, each of the quintuplets managed to pass their final.
In Chapter 55, Miku passes every subject, even English.
In Chapter 56, Yotsuba, the ditziest of the quintuplets, passes. She cries Tears of Joy while thanking Fuutarou.
In Chapter 57, Itsuki passes, and takes up a bold ambition to become a teacher like her mother.
In Chapter 58, Ichika passes, getting the highest score out of her sisters, even when she's saddled with being the quintuplets' main source of income.
In Chapter 59 & 60, Nino passes, and later declares her love to Fuutarou openly when the first time is interrupted by the wind.
In Chapter 76, despite being tired and sick, Fuutarou is able to place 3rd in the national mock exams. Even better, it is implied that the only reason he was not 1st was because he fell asleep towards the end of the final exam, and therefore missed the final few questions.
Takeda also has one by placing 8th place after tearing up the answer keys so he could try to pass with his own ability.
All of the quintuplets are shown to have passed, and it is mentioned how all of their scores have greatly improved from the previous year.
Before all of that Takeda challenges Fuutarou to make the Top 100. Fuutarou scoffs and says he can easily make the top 10, as well as continue tutoring the quintuplets. That's how confident he was at succeeding.
Nino calling out and confronting Ichika on the latter's behavior in Chapter 81.
The finale of the manga which takes after five years since their graduation, Fuutarou, who was initially couldn't differentiate the girls and even in Scrambled Eggs arc, he could only distinguish Miku (disguising as Itsuki) but even that he did it barely, can finally do so. Counts as heartwarming moment as well.
