I want a manga where the main character is good but needs to use evil methods or get help from evil to get stronger. I want an action manga so i dont mean that the main character uses tricks to beat people, i mean that the main character uses evil to get a power boost. Also, the main character still needs to remain good despite getting evil help. It would be nice if there is a little bit of a tranformation, like how Sasuke in Naruto got those black lines all over his body and then transformed or how in Inuyasha his eyes turned red and got a few markings on his face. One more example is how Maka from Soul Eater resorted to "insanity" to beat Chrome. If Aang from Avatar went evil when he went into his Avatar state then that would also be a good example.

mahou sensei negima.

negi gains this kick ass power that is evil and eats his soul.

[color=red]Edit by mod - Use Spoiler tags next time.[/color]

Hmm well Kurozakuro and Kiseijuu kinda? 😕
Hope it helps 😀

"Flying is learning how to throw yourself at the ground and miss." - Douglas Adams

Manga/Animelist

Kuroshitsuji
Diabolo

Both kinda work although no one transforms

Claymore
Shingetsutan Tsukihime <- Maybe?

"I've seen a look in dogs' eyes, a quickly vanishing look of amazed contempt, and I am convinced that basically dogs think humans are nuts." -John Steinbeck

Fullmetal Alchemist sounds like the obvious one
Vampire Juujikai, no transformation
Vampire Knight
666 Satan
Yu Yu Hakusho

Code Geass the anime

Code:Breaker http://www.mangaupdates.com/series.html?id=31871

u probably alrdy know this but Bleach has what u looking for

Ichigo turns hollow then transform into vizard

[img]http://s2.postimage.org/hmf63ku61/Nice_Scenery.jpg[/img]

Immortal Rain

Yuca is the BEST villian in the mangas that I've read.

The protagonist and the villian have both lived a long immortal life.(Yuca was reborn..and his memories of his past life was recycled into his new life..

Yuca (the villian) wanted to end this vicious cycle of life by plotting to destroy the world..you will feel pity on him. He's the BEST..Ever.

also recommend Saint Seiya, Red eyes, Saint Seiya - The Lost Canvas.

[img]http://i268.photobucket.com/albums/jj11/obinrobin31/FINISHED2-Roger.gif[/img]
[color=black]The Hidden Agenda=[/color][color=red]Gol.D.Ace[/color]

[color=black]This Week's favourite:[/color]
DoLL (Okado Tatsuya)
Xp

red eyes seconded
cant believe nobodys mentioned akumetsu
any code geass manga adaption (it seems there are several)
franken furan to a point
embalming - the another tale of frankenstein