From the introduction:
Have you ever dreamt of being a Hero? Of standing proud against the darkness in the night, of fighting under the moonlight in the name of justice? Or maybe you’ve thrown away those childish dreams, and know that sometimes you need to do things others will hate you for to save the world. Or maybe, just maybe, you don’t care about what anyone thinks in the first place, and just want to make things go your way no matter the cost.
Either way, welcome to the world of Duel Monsters. One of them, to be specific.