guiding hazard is a very good one! fluffy couple with good plot. my first one and introduces concept well! (finished)
dear, 00 is great just will break your heart. not as fluffy but that's cuz the plot is more serious than guiding hazard. (ongoing)
room without window has a side story that's guideverse. it's PEAK. you'll have to read the main story before reading the au to understand the characters but both the au and main story is PEAK 10/10 greatness. (main story (non-guideverse) is finished, side story (guideverse) is ongoing)
this is the most basic you could get i guess
https://www.mangago.me/read-manga/ordinary_daily_life_of_a_universal_guide/
https://www.mangago.me/read-manga/b_class_guide/
https://www.mangago.me/read-manga/conditions_of_a_guide/

Idk shit about the guideverse. Plz rec the best one to start with