That's a kind of illogical theory, though. It targets a player; players were originally--and have no reasonable analogue since--considered to be planeswalkers. As planeswalkers, this would make them magic users.Consequently, the logical sacrifice to unleash the demon is either 'planeswalker', 'powerful magic user', or 'magic user'. Conjecturing it to just be 'enemy' would have every summon transform the blade. >.>

... speaking of, told a guy about this card IRL, now he really wants to buy it. XD