As first thing, I want to say that Taku is the kind of character I like the most. The evil that understands his mistakes and changes himself from the bottom, becoming a person proud to be~

He's a kendo champion and a brilliant student, but later is revelaed that he got those goals thanks to the acceleration, so when he understands that he was using it to make his life simple, he can't bear the cost of success, and he decides to leave the things that made him a fake person, and he starts to work with all himself. The first thing he does is changing school, so he become a schoolmate of Haruyuki and Chiyuri.

Chiyuri... she's Taku's girlfried, but she's a stupid person that treats him like a normal friend (the best part of the time she seems to prefer Haruyuki more than him, LOL) or less than one of them... and she seems to have a crush on Haruyuki and not on Taku. So, even if it's said that she's his girlfriend, I can't consider her but an idiot. -_-

In the Accel World, Taku's identity is Cyan Pile. He's considered a traitor by his old team and because of this he's escluded by the region where he fighted.
For this reason and because of the green-eyed monster forwards Haruyuki, he try to fight and defeat Kuroyukihime and him.
The first one to retrieve the trust of his old comrades, and the second one to show him that he's better than anyone else not just in real life but in the Accel World too.

Then Taku lose.
Against Haruyuki and against Hime.
Haruyuki finds the real feelings of his best friend for the first time, but he forgives him from the botton of the heart, and asks to him to be his partner for the battles.
In a first moment Taku tries to help Haruyuki with all himself to lost all his points and to disinstall the program to expiate his faults, but thanks to Kuroyukihime's words (Chiyuri... where are you and your never existed brain, LOL?) he understands that he must go on keeping his past with him, not trying to cancel it.

And he really becomes able to change himself... for now~