Complex/slow-burning romance?

I'm looking for an anime, movie, manga, or LN where the relationship between the two leads develops slowly and in a complicated way - where they don't realize they're falling for each other, where their relationship deepens from friendship to love over time, and where it takes a big shock for them to realize how important they are to each other.

I liked these a lot:
-Spice and Wolf (slightly prefer the second season)
-Voices of a Distant Star
-The Place Promised in Our Early Days
-5 Centimeters Per Second
-Neon Genesis Evangelion Angelic Days

And I liked these slightly less:
-Karakuri Odette
-Ai Yori Aoshi (but only at first, before it degenerated into a "bunch-of-hot-girls-living-with-a-single-guy" thing)
-AI Love You (again, minus the overtly sexual parts)


I'd like it to:
-be serious and mature (in the "grown-up" sense, not the "explicit content" sense), but some lightheartedness is fine
-be pretty - nice artwork and attractive characters
-have at least a hopeful ending (but this is not required)
-sci-fi or fantasy is fine, as long as it isn't the story's main focus

I'd like it not to:
-be particularly sexual, unless it helps to move the story along (also, no same-sex couples)
-have too much slapstick or silliness


Thanks in advance!