Mine would be "Kill Everybody" by Skrillex. I've listened to that song over 500 times. And the song also goes great with my characters backstory >: j here's the back story
I was once the Royal Commander of my King's army. I was also his best friend, and he always came to me to get the job done myself if none of the troops could get it done... One fateful day came when my dearest friend became corrupt, and drove his kingdom into madness. The day came when the kingdom started a revolution against him. They stormed the castle... they brought with them rival kingdoms' Elite troops... They even brought in... ugh... The Nexus (The strongest yet cunning troops in the region... big bulky armor, one handed Claymores, and a menacing scream). They charged in; killing my best friend. In my rage I killed off all of their resistance. All i needed to do was to get his Queen out of the kingdom. I Bring her half way out of the Royal Escape Route, when her Royal Guard kill her... I wnet berserk; killing everyone in the kingdom. Still with all of that hate and anger inside of me; I discharged all my rage erasing everything from existence within a 50 mile radius.
Ten days later Luna found me in a crater 50 miles wide. She saw Darkness in my heart, black as night soul, and the desire to kill anyone in my way... no mater what the reason. She tells me "Come with me. The blood you thirst for; and the vengeance you seek will soon be yours. Just come with me, and I shall teach you the way...
I went with her, and she taught me all she knows about combat -Most of it I already know, like invisibility, duplication, heat vision, night vision, Assassin Rush, berserk, Spiral Inferno, etc.
One year later Luna makes me her Personal Royal Guard, and makes me do her bidding when she has more oppressing matter to attend to.
And don't try to use this as a story plot, cuz I have already done it, and got it reserved.