Forgive me for asking, but what's so difficult about doing it with Chiyuri?
Your own boss attack is a dice roll as she has attacks that shoot an ungodly amount of reflectable white pellets and the AI is a
master at reflecting
every single one back at you.
What you get as a result is a ping-pong match of 100 bullets going at 500 m/hour of which you will inevitably lose the match of most of the time.
Really, your own level 4 is your worst enemy.
Kotohime as the stage 7 decisive match is also the worst possible character you can get for that and she will rape you completely to shreds.
Chiyuri herself is also really fast which makes dodging hard sometimes and her level 1 charge is kind of bugged in that you can't bomb while it's active.
She just doesn't kill the opponent as fast. And I think I may just have to make this my next goal. This or 90fps EoSD.
Her killing time is moderate, there are certainly characters that take a much longer time. The issue with her is survival.
And good luck if you're going to try this because it's seriously a thing of ridiculous proportions. I'm not kidding. Clearing with Chiyuri is 10 times harder than with anybody else.