ダークスティールの反応炉 (Darksteel Reactor) (ja)
Artifact
(CMC 4)
Indestructible (Effects that say "destroy" don't destroy this artifact.)
At the beginning of your upkeep, you may put a charge counter on Darksteel Reactor.
When Darksteel Reactor has twenty or more charge counters on it, you win the game.