During battle, Samurai Jack accidentally swallows a piece of darkness coughed up by a sickly Aku. When Aku's blackness begins to take over the Samurai, he seeks help from Master Ning.
Did You Know?
Jack comes across a Dutchman hanging over a cliff on a snowy mountain, needing rescue. Under normal circumstances Jack would have rescued the man, but he was infected with the Aku blackness and left the small man hanging onto an icy stalactite. however Jack was cured of this later and was not seen (nor heard referencing) rescuing the man and apologizing. See more
You have been infected by pure evil which can only be purged by the light of good. The good within you.
References Princess Mononoke