Severe Spoilers Contained Herein.
From one of the great anime epics of all time, Neon Genesis Evangelion comes a single character who has caused plenty of debate and created a larger fanbase than most characters with more screen time in the series: Kaworu Nagisa, the Fifth Child, The Seventeenth Angel, Tabris. Kaworu appears in the twenty-fourth episode of Eva, as well as episode twenty-six (if I remember correctly) and End of Evangelion. We first meet Kaworu when Shinji has gone for a walk to try and escape some of the vast pain in his life. He meets Kaworu near the shore of the ocean or one of the Asino Lakes. (I'm not sure exactly which one it is) Shinji is at first rather suprised to meet a boy his age, sitting on a peice of debris from the explosion of Unit 00. Even more suprised that the boy is singing to himself, and the boy knows plenty about Shinji. When asked who he is, Kaworu replies: "I am Kaworu. Kaworu Nagisa. I am like you, one of the selected few. The Fifth Child." It is shortly after his arrival at NERV that questions start being raised.
Like the First Child, all of his records have been erased. The only record that remains is that of his birth - September 13, 2000. The same day as Second Impact. (This is the only birthday ever stated in the entire series. Although if you look quickly you can read Kensuke and Touji's in episode 4)
Commander Fuyutski starts to suspect something after Kaworu manages to synch with Unit 02 even before they have reconfigured the data. Misato goes to Ritsuko to ask if she knows something. Dr. Akagi replies that "He is probably the last angel." The doctor is correct.
Kaworu arrives in the cages and takes Unit 02, controling it from the outside. Shinji is forced to follow both the angel and his friend down the shaft towards Terminal Dogma, where Adam is. Upon entering Terminal Dogma (after breaking the lock with a mere glance) Kaworu discovers and reveals that the angel imprisoned there is not Adam at all - it is Lilith. Shinji arrives on Unit 02's heels, and Unit 01 seizes Kaworu in it's grasp. Although Shinji knows Kaworu is an angel, he hesitates to kill him - as Kaworu is also his friend. It is only when Kaworu states, "It is my wish, please destroy me." that Shinji is able to kill Kaworu.
It is after Kaworu's death what should have been cause for celebration is no more than the final trigger in the Human Instrumentality Project. If all the angels are destroyed, then the path to becoming one with God can be completed. There are two versions of this path, one in the series (my prefered ending) and the ending in End of Evangelion. Since I nearly went mad having to re-write the film ending in "Song of the Crane" (and that was without seeing the film) I am not going to drive myself further into insanity and spare you both. So just why do I have this extreme obession with Kaworu? You know, that's a good question. I nearly gave a hug to a guy cosplaying as Kaworu at Otakon. ~_~ I suppose its due to the fact is that he is such a likeable person - he's kind, sweet, tender - and so what if he can bring about the end of the world - given one of those worlds everyone save Shinji and Asuka end up as Tang, I wouldn't mind. You may find it odd that my favorite character from EVA appears only four times in my fanfics - and never in a major role. Well, just as soon as I can figure out a good little plot for him, he'll be the star.