I'm looking for a manga where the villian falls in love with hero. The hero doesn't necessarily have to be good like the one in Asterisk. They can have a twisted personality like in Legend of the Sun Knight. I looked through most of the starcrossed lovers category, but I may have missed a good one.

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I really like this one. A Fairytale for the Demon Lord. Although its a little confusing, bear with it and you'll get your obsessive villain doing anything to get his love interest.

Maoyuu Maou Yuusha - Kono Watashi no Mono Tonare, Yuusha yo Kotowaru - though the "villain" is arguably a good girl (so later on other new enemies appear to fill the antagonist void).

There is also stuff like Watashi no Ookami-san and Maou Voice, but again in those the "villain" isn't really a bad person.

Maybe one of those two could work somewhat: Mahou Tsukai Kurohime, The Legend of Maian