The manga you are looking for is titled Living Together with the Queen from My High School Days Who Was Arrogant, Surprisingly Isn't That Uncomfortable
The morning sun hit the cluttered floor of a tiny one-bedroom apartment, far removed from the marble hallways of Seiran Academy.
However, as they begin their cohabitation (dosei seikatsu), the protagonist realizes that the "Queen" he once feared or resented has changed—or perhaps he just never knew the real her. The "not so bad" (igokochi ga warukunai) aspect of their daily life provides the core charm of the series, blending slice-of-life moments with simmering romantic tension. Navigating "Raw" and "Welovemanga" Searches
Living with the girl who used to look down on him was supposed to be a nightmare, but as the steam from the rice filled the room, Sato realized it was actually… comfortable.