I'm looking for a very unique romance manga where the mc isn't the popular, perfect or arrogant shoujo stereotype. No harem or ecchi, also no webtoons or chinese and korean manga.
Something on the lines of Horimiya, which lately I've been wanting to drop because it became way too vague and predictable and Iris Zero. Any genre is fine as long as there's a serious relationship and romance, except for harem or ecchi again.

Koe no Katachi - They are quite young so the romance is very mild.
Orange (TAKANO Ichigo)
Kingyo Sou
Issho ni Neyou yo
Hotarubi no Mori e - The title one shot.

I made a nice long list but I had to remove a lot because they were webtoons. I see this kind of character a lot more often in Korean webtoons than manga (It's almost a webtoon stereotype). Though there is kind of a manga version of American Ghost Jack,

Kagen no Tsuki, but it doesn't fit as well (the character is not really the male lead in that one).

Koi no Katachi - They are quite young so the romance is very mild.

...BSDM yaoi incest? I think you have the wrong title.

Seconded on Orange, and also Ao Haru Ride.

Quote from meredithbecca

Koi no Katachi - They are quite young so the romance is very mild maybe a typo and it has to be Koe no Katachi?

Tetsugaku Letra
Kimi wa Pet
Itoshi no Karin

Quote from annebel

maybe a typo and it has to be Koe no Katachi?

Tetsugaku Letra
Kimi wa Pet
Itoshi no Karin

Sorry, that's what I meant. Thanks. It was a typo.