The dramatic shift in power during the graveyard episode when Aku nearly kills Jack with his own sword. After the reveal that Jack's sword won't hurt the innocent, Jack gives a badass boast.
Aku: [After he loses the sword to Jack when it fails to kill him] How?! HOW?!
Jack: Even I had forgotten that the sword was forged in purity and strength. It can only be used for good. In the hands of evil it could never harm an innocent! And so, Aku, it cannot harm me... but it can harm you!
- Aku himself had been dominating that episode by really showing off his might: he provides quite a bit of awe in that episode too.
- Not to mention the sheer tenacity with which Jack fends off Aku's attempts to kill him.