It's the first time Klein has ever stepped foot into the Not Ranked Duelling League, and he's keen to make a good first impression. His opponent being a final boss, and him being a main character from his own native game? We all know how that turns out. Thanatos' best attacks are Dark and Lightning elemental, both of which Klein resists greatly. MP draining? Not a problem. Klein's plentiful MP, along with Divine Shield, renders Thanatos powerless against him, and his own supply of offense and healing never runs out. Heck, Thanatos being undead and weak to light gives Klein all the more choices, as Heaven Geode is light elemental and only hits the undead. Wonder if he can alchemize something out of a dead last boss?