That's the title of the south park episode where Stan, Kyle, Kenny, and Cartman get weapons and dress up as ninja. During the episode, the kids' imaginations run wild and the animation is anime... esque.
I know this episode is kinda old, and it isn't
really an anime, but I saw it this Thursday and it's a pretty damn funny anime satire.
Here's a pic of all the characters as "ninja":

From left: Kyle, Kenny, Stan, Cartman (kinda obvious)
Here's a link to my favorite scene, where other kids get weapons and they fight Stan and his friends. It's cool how the song sounds like an actual anime theme(except for the "protect my balls" part):
YouTube - South park-ninja fight
I think Kenny and Craig are the coolest.
NOTE TO MODS: Move this if you want, I didn't know where to put it.