im looking for a manga where at least one of both, hero and heroine, hates the other to the point of wanting him/her dead. and i actually mean dead so not some simple grudge because for example jealousles because the other is more skillfull or just kind of arrogant.
then later on that hating character developes feelings for the other side for whatever reasons..

no yaoi yuri ai hentai everything else is fine
thanks

Basara - They are in love with each other but also enemies, however they don't know it.
Kare Kano - but only for a few chapters and it's quite a weak hate.

perhabs Superior? The MC doesn't know that the person he loves and the one he hates are the same though...

I predict Big Order will be what you are looking for but, well 2 chapters so far... So don't take this too seriously...

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in need of romance?
uncommon, sad, sweet

I'm looking for the same thing! Like actual hate not just dislike/annoyance. For example, something must have happened in the past to cause the hate... ie they have a "history."

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Favorite Shoujo mangaka:
TAKANO Ichigo
Robiko
IKETANI Rikako
ASHIHARA Hinako
YOSHINAGA Yuu
AOKI Kotomi

Favorite Shoujo Scanlation Group:
Forbidden Garden

I second Superior and Basara.
And I think Chang Ge Xing is pretty much going in that direction.

The Bakumatsu chapters of Rurouni Kenshin is exactly this, though it is only a small part of a bigger work.

Doupo Cangqiong there are more than one heroine so probably not what you want
Spirit Circle it's a bit complicated but it kind of fit :/
Kubera seems to go the other way around - from love to hate... but still not sure where things are going.
The Pale Horse From love to hate and again love with a bit of revenge and angst and stuff.
Jewels
Trace it's about two of the side characters. Girl get close to the guy in order to get revenge.
Suikoden III but it is more like friendship that may latter become something more.

Superior and Basara x3

I suggest Legend of Nereid and Reimei no Arcana. You can also try a genre search with a category like "Enemies Become Lovers." Here is a search I set up with that tag which excludes yaoi/yuri/hentai.

I also have to to suggest Basara and Superior. They both are very good and are prime examples of what you are looking for I think. I also like these types of stories, more specifically I like a strong female warrior story. Here is a post I made in another thread with a small list of them.

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How lucky I am to have something that makes saying goodbye so hard." -Winnie The Pooh

"As through this world you travel, you'll meet some funny men; Some will rob you with a six-gun, and some with a fountain pen." - Woody Guthrie

No man chooses evil because it is evil; he only mistakes it for happiness. - Mary Shelly

Everything happens for a reason and that reason is usually Physics. - Anonymous

Vampire Juujikai - hate + reincarnation = fun times

Pretty sure Samurai Deeper Kyo had something like that.