So, I'm looking for a manga where the main character is potentially evil/dangerous.

Like, in Dragon Eye

How not only does he go on a murderous rampage whenever he gets hurt, but when a seer "sees" him all they see is a monster. but he still acts normal-ish and not-evil. Preferably lots of flash-backs/character development, since that is what I like best.

Or in 666 Satan how he is when

He transforms into Satan

So, basically, where the main character normally has a pleasant attitude (Faked or otherwise), goes all bad-ass and Berserk.

Does the walker choose the path, or the path the walker?

So you mean not completely menacing, but actually nice/normal people who can become threatening occasionally?

Beast Master - the male instinctively goes "beastly" when the girl is threatened
Kanata Kara - Izark has the sky demon that can destroy the world within himself
Naruto - Naruto has the fox demon sealed in him
Lament of the Lamb - the male violently craves human blood from a disease
Onani Master Kurosawa - not sure if this fits, but his dark emotions can lead himself to sexually harass others
Pieta - the main girl is psychologically unstable
Majin Tantei Nougami Neuro - Neuro solves murders, which I guess is good, yet he manages to make people miserable... xD
Suzumiya Haruhi no Yuutsu - if Haruhi gets bored, the world will be destroyed
Tsubasa Reservoir Chronicle

The Syaoran at the beginning is actually an evil clone of the real Syaoran and later betrays the whole cast against his will.

I feel as if there are some obvious ones I'm missing. I'm sure there are, too. =/

Samurai Deeper Kyo

Lalala~

Lelouch

"I am the bone of my sword.
Steel is my body, and fire is my blood.
I have created over a thousand blades.
Unknown to death.
Nor known to life.
Have withstood pain to create many weapons.
Yet, those hands will never hold anything.
So as I pray, "Unlimited Blade Works."

Quote from drolemil

So you mean not completely menacing, but actually nice/normal people who can become threatening occasionally?

More like they are dangerous/evil, they just don't act like it.

Thanks for the suggestions, everyone. I've read most everything, or dropped it, but some things I haven't read.

Does the walker choose the path, or the path the walker?

For anime, watch Darker than Black.

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Meybe Lost+Brain

Code Geass (the Anime), Lelouch is not directly evil, but as he says:
I´m willing to comit evil to destroy the greater Evil, and he is also willing to sacrifacie anyone or anything to achive his goal. This anime is GREAT.

Gamble Fish he is not realy evil, but he is a gambler/swindler, And he is the brain type.

And Death Note, He is, well, not evil, just Wicked.

If you want to succeed
Then you don't need Good Luck
You need the ability to overcome Bad Luck

Happines and Light needs a source to exist
Hatred fuels itself and Darkness exist where there is no Light

[img]http://www.nodiatis.com/pub/7.jpg[/img]
† Lightmare †

you said potentally so here are a couple mangas i've found that have that potental but i don't any of them are complete
the breaker (korean) - the main character is the typical bullied kid who grows unbelievably strong really fast. his teacher seems like a goof but is one very scary guy when he gets going. (i am totally in love with his badass teacher).
dance the vampire bund - a werewolf main character and a vampire love interest, how could he not be badass?
alfame inferno - high school guy has a demon inside of him. when they merge he ends up looking (a little bit) like the main character from the smt:nocturne game.
psyren - i just started this one but so far he seems kind of bad ass, but ends up awakening psy powers.

it almost seems like your looking for double life kinds of manga. on the surface everythings normal, underneith is chaos. i like those too.

a couple light ones with the same theme
D.N.Angel (he has "dark" inside him).
kateikyou hitman reborn (wimpy kid is 10 boss of the vongola family...gets better around vol 8)

Shamo

half the time you like him and think he's a great guy... the other half you think that he is a really bad guy... there's a scene early in the manga that is a little disturbing though, but get past it!

highly recommended by... me!

Code geass zero/lulu/lelouche however lol
then theres deathnote personally i thought his idea of purging the world of evil wasnt too bad a idea
hmm there are others but i cant simply think of it .
ah there is also code breakers thats a decent one ill edit if i can think of more i know quite a few just not off the top of my head

Fate does not coming knocking at your door but rather it is you who is knocking at fate's Door.
[img]http://i299.photobucket.com/albums/mm282/pureluck197/THeforfunsig-1.jpg[/img]

I've read/watched all of the things suggested, but thanks anyway!

Does the walker choose the path, or the path the walker?

Heads possibly.

Thanks! It looks almost like what I'm looking for, so far; its kinda hard to tell, though, since there are one 2 chapters out.

Does the walker choose the path, or the path the walker?

Do you mean you want yandere types or do their evil deeds never slip to the general public?

Bunch of people in Alive, some are more scheming and some are just stepford smiler types.
Sin Uoo Park from Hot Blooded Woman and also

Han Seo though he wasn't a nice guy to being with.

Russia/Ivan from Hetalia...if you consider him a main character
Seras Victoria of Hellsing (and Intregra, and Walter)
Sebastian of Kuroshitsuji
Shirogane of Monochrome Factor
Count D in both Petshop of Horrors and its sequel
Abel Nightroad of Trinity Blood who appears to be an idiot hero like Kenshin and Vash. Train of Black Cat too. Fire Emblem - Hasha no Tsurugi also has a main character like that (though the dangerous part is kind of a spoiler).
Love Monster with its badly rushed ending delivered a moment of this as well.