At the end of the AA/A routes, Takumi gets killed by the Big Bad and after a series of questions concerning his identity and status as a delusionary being, starts regenerating no matter how many times he's killed until he finally destroys Noah II.
In the climax of Sena route, Takumi's DI-Sword becomes gigantic and so powerful that he and Sena menages to destroy Noah II and kill Norose from afar with a single swing — at the same time they're being gunned down by a mind controlled mob.
In the anime, after 10 episodes of being a pathetic loser Takumi becomes.... well, still a loser, but a dangerous one who pulls off some of the shows best moments. In addition to the scene mentioned above, he also takes out that psycho Suwa by essentially turning his own mental attack against him.
