The Perfect Relationship
Sadistic Beauty BL Sidestory
EDIT: btw if u dont like romanticizing toxic behaviours don't get roped into reading the fanfic lol it's worse than the side-story itself and not even well written, you're better off reading the webtoon or not reading about them at all Idk why would any of you see this as "romanticization". It was never portrayed as anything but an abusive relationship with a huge power imbalance from the very start. It's clearly shown that the situation is fucked up, do you really need the author to spell it out? Even just the art communicates it, e.g. with the facial expressions. One of the characters is shown as mentally unstable and violent and the other understands the situation and even realises that they are being manipulated. There is literally no space to read it as a wholesome healthy romance. Actually, after the main story how would you imagine it to turn into a romance in the side story...? That would be way worse imo.
Akuma-chan wa Momoiro