The song is "We Are!" 4kids also has a version, but it SUCKS. This one is much better, especially considering it's sung by the one and only VIC MIGNOGNA! =D
Here are the final four songs of the Soul Eater soundtrack. Songs: Track 17- Selenic Soul; Track 18- Blitz; Track 19- Death the Kid (So Crazy); Track 20- Bang! Bang! Bang! Bang! Have a Nice Dream.