It's hard to explain, but the best example I can think of is of Rebel: Thief Who Stole The People. Romance wasn't the leading genre and neither was it very apparent, but just from the nature of the lead couple's relationship and from their interactions I couldn't help but ship them very hard. It didn't feel like they were together because they were the leads, but it was more like they were together because they fit each other's personalities and characteristics. Chicago Typewriter kinda fits the bill as well, but the romance wasn't as quite as memorable as Rebel's.
A few requirements: A happy (not open) ending and no love triangles unless it's minor and doesn't take over the romance for the rest of the show.
*When I mean subtle, I don't mean something that hints at a romance. Romance still has to be a genre, I just don't care if it's a side or main genre.
Sorry if my request is too hard, but I've just been craving something like this for a while now.