Shinji is Lakan's leader. He believes in the free will of people and that is what his group is based on. He is rather carefree, but believes very strongly in his ideals. He's basically a younger, rasher Oonishi, and could probably be considered the third protagonist of the series.
His best friend is Haru and his girlfriend is Yoko. However, Yoko and Haru are also intimate with each other; Shinji explains that since their group is based on free will, it's up to Yoko to decide what she wants to do.
He first takes Yoshii in near the start of the series when some of his guys get their asses kicked by him. Later, he accepts Ichise and Ran in and help Ichise learn to control the sensitivity of his Texhnolyze. He is then betrayed by Yoshii when Yoshii sets up a bomb in Lakan's main headquarters. As a result of the bomb, he targets Oonishi and gets his men caught up in a fight with Oonishi and the Alliance.
Eventually he comes to learn that it was Yoshii who set everything up when Yoshii takes him along for his assassination attempt of Class Dude. When Shinji learns what is really going on, he tries to stop Yoshii, but is stopped himself by Tatsuya. He makes his escape while Yoshii is trying to assassinate Class Dude.
Later, his men start leaving and disappearing due to the appearance of the 'ghosts' (Shapes). When his member count starts getting low, he kind of gives up and goes out. He meets Hirota on his walk and they have a short date. She tells him that she respect him for trying to be like Oonishi.
When he goes back, Haru and a few of the men have decided to leave. He can't get a reason out of Haru, but Haru tells him that he'll kill him the next time they meet. When Haru does come back, he's a shape and he says that Shinji isn't worth his time to kill any more. Shinji, however, sets up a fight at their old headquarters.
Haru tries to show Shinji his new power, but Shinji continually shows him up. It's finally revealed that Haru just wanted to be stronger than Shinji. Shinji eventually puts him out of his misery by sticking his Texhnolyzed finger through his eye socket and into his brain.
He then heads off to find Oonishi and meets up with him at the tunnel to the Class. From there, he goes and meets with the Mother with Oonishi, who tell them that they have to warn the upper world about Kanno's plans. He returns to Lux, however, because he says that he wants to be the one to kill Kanno.
He helps Oonishi gather the men together for a final battle with the Shapes in order to take back the city. They're successful in doing so, but at the cost of many lives.
Sadly, however, no one told him that Kanno was shacking up at the Opera House. Instead, he gathers some firepower and heads to the gate where he met with the Mothers. He blasts his way through to a group of Mothers and destroys them before he is shot in the chest by Blind Guy.
