A manga with a guy trying to win a girl who initially sees him only as a friend. Anime are welcome too.
Examples would be Sakurasaku Syndrome; Tonari no Kashiwagi-san; Uwagaki
If it's a completed manga, that's a plus. Completely scanalated ---> even better XD
It's ok if it isn't the main focus of the manga, as long as this theme has decent space, and it's fine if this happens to secondary characters. I've searched other topics, but they hadn't these conditions:

-no harem (meaning no more than two girls/guys for the same character)
-strictly about boy pursuing girl, not other combinations
-if you're going to suggest a shoujo (don't know if it's possible), please avoid the jerk/playboy/supercoldbuthandsome/etc. male lead
-not strictly required, but not too much fanservice would be great

Thank you for reading this, have a nice day!

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My current top 3:
Fullmetal Alchemist
Pandora Hearts
3-gatsu no Lion

Gokusen - completed
Last Game - ongoing
Miman Renai - completed
Sekine-kun no Koi - ongoing
Watashi no Ookami-san - completed

Hope this helps

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This, I second heartily!

~~Dos

You set your bar pretty high with those examples

Maybe you could try High Spec Lovers, though it's only a oneshot

Gotta agree with you jahu
I've read that oneshot not too long ago, and even though it doesn't exactly fit, I really liked it, so other works like this one are completely fine.
Also thank you bakerygirl and Dosudro, I'll check all these manga (maybe except Miman Renai, since I'm not really comfortable with the subject).

Any other suggestion, from oneshots to manga with 100+ chapters, from anime series to animated movies, is more than welcome!

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My current top 3:
Fullmetal Alchemist
Pandora Hearts
3-gatsu no Lion

Tenshi na Konamaiki should fit. It's very long and complete (20 vol), and has a good anime adaptation. Romance isn't the main genre, but rather comedy. Genzo tries to woo the female MC the whole time and it's really funny.

Nineteen, Twenty-One though the romance is slow and understated.
Honey (MEGURO Amu)?
My Hero!
Joou no Hana
Sakamichi no Apollon or you might want to watch the anime (the soundtrack is incredible).
Koi Koinegau oneshot
Joyful Days? oneshot

Even though you wrote no harem, you might want to give Tokyo Innocent a try. It fits your request somewhat and the style is quite different from a typical harem.

Again thank you for all the suggestions!! I'll check Tokyo Innocent too, after all no harem can be more "haremish" than Nisekoi, and if I can stomach that one...

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My current top 3:
Fullmetal Alchemist
Pandora Hearts
3-gatsu no Lion