It wasn't that she underestimated him, she was just that confident that she already had him all figured out, and to prove it, Akiko avoided his strike with a simple step to the other side, followed up by a knee strike directed to his stomach. No matter how much Kanji grew on her, she still wanted to end things, no longer having the patience to hold back.
If she managed to hit his abdomen with her knee, Akiko would follow it up by stunning the Emperor with a Front kick that went for his jaw. The relentless girl would stop for a second, to check on his response to her siege. A couple of cold, ruthless and simple words left her lips as she checked her work...
Spoiler
"Suit yourself..."
