OhEmmGee... I so wish this was real! I can imagine streaking your stylus across the screen to slash someone's throat... Yay.
I suppose the warnings for the rating would be... Blood and Gore, Intense Violence, Sexual Violence, Strong Lyrics, and Violent References. (And that makes it ALL THE BETTER!)
DS Template from

ESRB Rating Tab and warning terminology from
[link]EDIT:<b/> Since almost all of the comments I've gotten so far can be summed up as "OMG It's so good! I wish it were real! lolololol", I've disabled them. Hello, good bye.