I'm looking for a manga with characters who go through normal life, thinking that everything is meaningless, because he/she obtained knowledge about the hidden realities about the world he/she lives in. After obtaining his/her power, he/she no longer go back to the normal life he/she once led. He/she is forced to go through trials commanded by his/her superiors, while living a hollow school life. Even if the things he/she does is good for the people, they won't know that. The things he/she does at school are easily misunderstood, just because he/she is stronger than anyone else. When the character don't care about anything, they are downright cruel, when it comes to their secret assignments.

But things start to change for the character; for a fated meeting from an old friend, or a complete(and energetic) stranger, he/she starts to become more adaptive to his/her surroundings, and school, even accepting the power he/she possessed as a gift instead of a curse.

Wow, I sure ask some weird requests. But I do wonder if this sort of thing exist. The character don't have to be a complete pessimist, they could have some embarrassing secrets as well.

[img]http://i30.photobucket.com/albums/c303/jasonpark1987/0c01ca55-eed4-4af9-a361-1d424276fe1e.jpg[/img]

Wow, talking about a detailed request...

I don't know anything as that, so I'll just tell you the most similar settings I know...

World Embryo Con: not really school life. not cruel.
Spiral Con: not superiors. not stronger but more intelligent.
They're both very good for the second part of the request (fated meeting).

And maybe Kekkaishi but I gave it up too soon to be sure.

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

psyren?

Code Breaker
Busou Renkin had something kinda like that but in reverse.
Hitsuji no Uta

I have six locks on my door all in a row. When I go out, I only lock every other one. I figure no matter how long somebody stands there picking the locks, they are always locking three.

P.S. Dead Fantasy. Look it up.

katekyo hitman reborn

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

[img]http://i707.photobucket.com/albums/ww73/chewy_bubble2004/2d360793.gif[/img]

If you don't mind a romance, try Her Majesty's Dog. It has some of those elements.

Might not be exactly what you are looking for, but they contain most of those elements:

Lost + Brain: This has thinking everything is meaningless, assuming better knowledge, and obtaining power, etc. May not have fated meeting though.
Nabari no Ou: has a fated meeting with a complete stranger and is overall very close to your plotline.
Angel Sanctuary: sort of fits too, esp. the "no longer going back to the normal life, fated meeting and accepting power" parts.
Nephylym: also has a main character who assumes a better knowledge, school life, obtaining power, doing good things which most people don't know, and sort of a fated meeting.
Dokebi Bride is almost exactly the first part of what you described, and will be likely to have the second part though you can argue whether there's a fated meeting.

one outs

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

[img]http://i707.photobucket.com/albums/ww73/chewy_bubble2004/2d360793.gif[/img]

Those listed are good but... the best one that describes what you want is The World God Only Knows