- If Mariko can kill the hero in one hit, why can't she just escape herself?
- Because she doesn't kill the hero due to her overwhelming martial arts ability, she kills the hero because he doesn't expect the attack - the same reason any enemy can One-Hit Kill the hero if he's not in fighting stance. Presumably her guards would be much less trusting.
- Also, the hero is short enough such that Mariko could kick him in his One-Hit Kill spot, whereas the Big Bad is too tall for that to work.
- Who says she didn't try it? Maybe Akuma had Balls of Steel.