After the original 3 volume run in 2020 Niiyama got her own epilogue volume in 2022, showing she was aimless after her sexual escapades with Iida left her a little empty, she enjoyed sex as much as Iida but Niiyama actually wanted a boyfriend.
A new character is suddenly introduced, Souta, Niiyama's childhood friend whom she couldn't imagine would grow up to be that dashing, he is a handsome and popular and confessed to her but Niiyama felt she was too dirty at that point and refused, going for an old crush of hers that just wants casual sex, but said crush didn't think much of Niiyama, he even allowed her to taken by his friends, which Niiyama didn't want to so she was raped.
Souta heard of this and beat up several of the guys who accosted Niiyama, getting suspended from his school volleyball team after that, Niiyama hears of this and her feelings for Souta soared, slapping her crush for being clueless why Souta beat him up (he doesn't think sharing her was rape). Niiyama runs for Souta and now accepts his feelings, the end of this epilogue shows Niiyama married Kouta, and he became a pro volleyball player.
The new 2026 Karami Zakari release further asserts how much of a happy ending Niiyama got, in the class reunion it is mentioned she has a son with Souta, the boy seems to be old enough to be 4 years old or so, confirming they got married and started a family pretty quickly after graduating and have been tight ever since, Niiyama's former classmates all tell Niiyama how lucky she is to have a star volleyball player as her husband.
Niiyama's happy ending doesn't feel all too hamfisted beyond Souta being introduced out of nowhere, but it is good nonetheless as Niiyama got her life back on track and made a conscious choice to be with her charming prince, after making the mistake of rejecting him once, before she was lost for good as an easy lay for guys to have casual sex with like Iida.