Umm...wow...
Besides the fact that insta-kill cards are generally frowned upon this seems pretty overpowered. Especially the cost.
Personally, I don't very much like that mechanic, but if you were going to modify it, I would suggest upping the price, perhaps having it drain all light quanta.
I'm probably going a bit overboard, but I dislike insta-kills.
EDIT:Sidenote: cool art, cool name, and now that I think about it, not a bad mechanic. Not necessarily a great one, but not bad.