well, you know the heroine is falling for a nice and handsome (perferct??) boy and then she discovers that he has a double personality: player and kinda cruel (kinda like the first volume of moe kare before knowing that there were actually brothers)

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um DNAngel

^ Eh, I wouldn't say D.N. Angel entirely has a double personality. It's more like two souls sharing the same body, hence "D.N.A. change". But yeah, I guess you can say it looks like a double personality since Daisuke and Dark's personalities are really opposite from another.

Double personalities aren't that hard to come by in some manga but they come in different forms. It depends on whether the mangaka goes with the split personality, hide behind a mask, or the twin brother approach.

Shinshi Doumei Cross - involves

twins .
Imadoki! - involves main guy having to hide something from the rest of the school.
Moon Boy - involves main guy with split personality. One is gentle and meek. The other is the exact opposite.
Skip Beat - involves main guy having to "act" out as another person.

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"You're so cool" matches that perfectly~

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Megane Ouji - Heroine meets two boys and they're actually the same person.
I second Imadoki! and Skip Beat!, as well.

Haou Airen maybe?

Glados is a bitch. She made me kill the companion cube, the only friend I'll ever have. 😢

Chibidoro-sama=Neko-freak

Skip beat, D.N.Angel and Shinshi Doumei Cross: already on my wish list
Haou airen (when I remember this manga I feel like killing somebody >:-( ) and Imadoki: on my unfinished list
Megane ouji, You're so cool and moon boy : I'll check that out!

And thanks everyone ^^

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You could try MPD Psycho, it's not shoujo though, quite explicit with little focus on romance.

man... main character had multiple personality in MPD Psycho >_>

no one else mentioned Elfen Lied? eh...

known as Lucifer / Killy69 / Guts / L41n / Lain Iwakura / Schrö.

A GUY, not a girl

A just ruler amongst tyrants

Jikiru de haido na karec, it's a short story.
S+M, but that's more like Moe Kare.

light from death note
good and evil weeee

La Corda D'Oro - The double personality guy is sorta leaning more on side character, but there are moments still the same.

[img]http://i56.tinypic.com/acfmfo.png[/img]

Perhaps Jikiru de Haido na Kare though the guy is a strict teacher and the other personality is flirty, not cruel or anything like that...

Life's not about waiting for the thunderstorm to pass... It's about learning how to dance in the rain

Give a man a match, and he'll be warm for a minute, but set him on fire, and he'll be warm for the rest of his life.

[img]http://i9.photobucket.com/albums/a77/YamiNoRyu/tetona.jpg[/img]

Well... i dont know if its exactly what you want ,but you could try [Ranma 1/2](http://www.mangaupdates.com/series.html?id=1049). The guy changes to a girl when he touches cold water, and back to a guy when its hot.
I dont think you can expect to get a "good" romance out of it (after all thats not
the point in it) but it can offer you much laugh and relaxation for a long...long time.
Even after so much time, nothing can beat a classic 😀

Mittsu no kokoro ga hitotsu ni nareba...
Hitotsu no seigi wa hyakuman pawaa.

• Getter Robo -