For me, it's when the romance develops naturally. I love watching the characters slowly understand each other through small moments and conversations instead of falling in love all at once. That gradual growth is what makes a route stay with me long after I've finished it.
I completely agree! I love a naturally developed romance instead of insta-love tropes where the heroine or usually the LI just falls in immediately. And I love little scenes that demonstrate how MC and the LI are actually emotionally compatible and a good fit for eachother in terms of their values or interests - it feels like wow, these two would actually make a strong long term relationship work and that the relationship is not just built on physical attraction!
like for example an LI is talking about a certain principle or goal he has, maybe he's really ambitious and has big plans for the future, and the MC might respond with how she admires people like that who have a strong drive and how it inspires her to keep working towards her goals too!! Small stuff like that is so cute