Character

Shinji Ikari: Throughout the series, Shinji is a very troubled individual, but most of his situations are either caused or further worsened by his extreme lack of self confidence. Shinji finds it very difficult to express his emotions to others, and is very often unwilling to adapt to his surroundings.
Also, the fact that Shinji has a terrible relationship with his father, Gendo, as well as losing his mother, Yui Ikari, at a very early age, haven't made his life any easier. Unfortuanaly for Shinji, running away from his problems is one of his traits, one which he must over come to lead a less stressful life. Unable, or possibly unwilling, to bear the company of his father after spending many years exiled from him, Shinji instead decides to take Misato Katsuragi's invitation to live with her upon his arrival in Tokyo-3. Eventhough Misato isn't the ideal roomate to say the least, the odd situations he's thrown into as a result of living with her help him open up a bit.
Shinji is also the reluctant pilot of Unit-0. Eventhough no one really knows why Shinji continues to pilot the Eva, but he has made it clear through his words and actions that he'd rather not be it's pilot.

Rei Ayanami: Rei is extremly timid, shy, and at times seems withdrawn from the world around her. Not unlike Shinji, Rei finds it hard to express her feelings twords others, and as a result, doesn't make friends easily. All of Rei's personal information has been erased. She has no parents and there is no trail to her past. It would seem her existence starts at a dead end..
Rei was the first child chosen to pilot an Eva, Eva-00 in particular, in accordance with the Marduk institute. Though Rei was severly injured during the first run of Unit-00 after it mysteriously went beserk. Fortunatly for Rei, Commander Ikari was able to free Rei and rehibilitate her. Upon her second attempt to pilot the Eva, the sychronization was succecful, and Rei is now the active pilot of Unit-00. Wether or not Rei actually wishes to pilot the Eva is unknown, Rei seems to do whatever she is told without complaning or asking questions, something Shinji is also knwn for.
The fact of the matter is, though, Rei is not human, at least not compleatly. She is a by-product of the human instumentality project, artificially created and implanted with the soul of Yui Ikari. Rei has only one soul, however, NERV has created many bodies, or vessels, for Rei in the event of her death. Rei is killed twice, once by Naoko Akagi, and the other time by the sixteenth angel.

Asuka Langley Soryu: Asuka is very confident in herself, and constanty tries to better herself over others. Ever since her mother, Kyoko Zeppelin Soryu, went insane after an accident in which she tried to synch with Eva-02, and commited suicide many years earlier, Asuka has had an extreme pride in herself, which could be a way for her to deal with her loss. As a result, Asuka is almost always unwilling to accept help or advice from others, and will rarely admit to making a mistake. She can also be very annoying, and often looks down on people, especialy Shinji, but would never intentionally hurt the feelings of others.
Since moving to Japan, Asuka has taken up on Misato's hospitable offer and chooses to live with Misato and Shinji, but with Asuka's fondness for Kaji and her overall attitude twords Shinji, Misato's appartment has become consideraly louder since her arrival.
Asuka is also the proud pilot of Eva-02, and is probably the only child that actually enjoys and takes pride in piloting the Eva. Unlike Shinji, Asuka is a not a naturally talented pilot, which is probably the reason for her persistant rivalry with him.