The hero meets a character who is unsure whether is he/she is a friend or foe, due to their carefree personality. When the story progress, the character begins to show his/her true color. But even when their plan goes awry, it does not seems to concern them, since he/she doesn't even care whether the plan he/she is carrying out succeeds or not. Whatever the motive is, even if the he/she fails, he/she will try again eventually, since this is all he/she exist for.

I don't see many villains who accept their loss after a battle. There is just too many scenes when the villain desperately tries to attain their goal, even when they can no longer move.

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Quote from Karis

he/she doesn't even care whether the plan he/she is carrying out succeeds or not.

Quote from Karis

Whatever the motive is, even if the he/she fails, he/she will try again eventually, since this is all he/she exist for.

I'm not sure I understood it right. You mean something like it's fate that he/she has to keep doing that? Otherwise I don't understand how a character could not care about his/her plan and this plan be all he/she exists for?
Anyway my first recommendation is Vampire Juujikai. Due to a curse all the reincarnations of the Black Swan will keep fighting the king vampire until one of them will win. But they do care about winning (sorry, I don't understand how a character could not care about his/her goal).
Or maybe you meant something like Superior in asking for this?

What I like in Trivial Pursuit style. Pick your category:[img]http://i379.photobucket.com/albums/oo233/Reid4891/Manga/trivia-1.jpg[/img]

The blue king in Basara is kinda like that. At any rate, he doesn't keep on going on and on when he loses; he just moves on to the next plan. Which is what you mean, I think? (Like Plankton from spongebob?) The main characters also don't really know if he is friend or foe.

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

juu oh sei

Code breakers

why because i am the president of the student council of course

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Kampfer <== sorta?

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Tyki Mikk from D.Gray-man sort of fits the description throughout most of the storyline.