Starting from boy meets girl we see in the manga, then the story of these two's past quickly came up to be resolved
MC familes passed away in car accident, and he had to be the one ending life support for his sister. He got back on two feets with his Uncle's help, but middle school idiotic rumors made things extremely difficult for him he end up behaving like we see here
FMC has parents about to get divorced, while also used to have to deal with too many flock around her for drama due to her being simply "too beautiful". Lost nunbers of friends in middle school, again, from idiotic rumors that spun out of control (Her NTRing other couples) and led to her being like present, trying to please everyone.
It gets a bit worse. While FMC mom was admitted to the hospital, her dad came unannouced and tried to coerced her into living with him. Said lots of stuff that crumble her last good image of her dad. MC help her get away from the house and they got together after that quite quickly.
Due to that circumstances, their relationship fast tracks into cohabitator, skipping a lot of awkward teen romance stuff due to both MCs being high spec in their own way. Big stuff happen during winter break (yup, stuff you see in the other spoiler - segg), and then we reach the point we see in early pages of this manga. (Their relationship begun and grow within Autumn and New Year. Fast, but not too unnatural)
What happen after is now closer to Fragrant Flower. With strong bond of the MCs (they are literally old married couple level now) and solidify their life outside of school, the story shifts to develop them fitting in their highschool more. There is huge mess of relation between FMCs's friend group and other people in and out of school, which the story focus on developing their characters while showing steady intimate moments of the MCs. Oh, and don't worry about the No.1 guy. He is indeed really sweet and endearing, and become fast friend with our MC after New Year.
Up to Vol.4 of WN that I read, this whole main group of friends expands to 8 people with several other relations outside the group. Turning full Fragrant Flower where the group band up to solve each other problems and issues.