The Rose-Nasty, the pink Dual Wielding beam katanas. The fact that it is given to you by Takashi Miike (as himself) only extends the threshold of awesome as you bisect mooks.
After defeating Alice, Travis gives one of the best speeches in the game, realizing that what he's been doing has been downright awful and that his fellow assassins were humans instead of toys. Ending with him screaming at Sylvia about how she forgot about Alice like she did about him.
What's better? He ends the speech with vowing to tear down the UAA and planning to become a hero on his own terms, making sure that no assassin ever goes through the type of torture that he and all of his opponents again.
While Shinobu's fights with Million Gunman and New Destroyman could have been a bit more polished, the way she takes them out is simply glorious.
For the latter, it also has a Call Back to the first game where Destroy Man insists that he and Travis shake hands as a sign of sportsmanship, then electrocutes him. When he tries the same thing with Shinobu, she cuts his hand off before he can do anything to her. At the end of the fight, she says that she really did fall for it.