Oh wow I missed that, thanks for catching. Given these are Japanese macaques, it looks like typical m/f size difference is more like ~32%, not ~45%, and 10kg puts her larger than the average female, but smaller than the average male. Would be interested in the former alpha males size too, but it's probably safe to assume he was bigger!

https://en.wikipedia.org/wiki/Japanese_macaque

Well it does say that she roughed up the previous alpha male, so presumably she's at least similar in size/strength.

She's also 22 years younger than him.

You inspired me to the lifespan of Japanese macaques, and it is 27 years; the previous alpha male was 31 years old, which suggests to me that he must have been pretty over the hill.

Given that she is smaller than the average male macaque, I imagine that this is not a terribly stable situation.

Interesting. What are the odds they can set up a livestream so we can watch macaque fight club? I love a good underdog.

I heard yakei was doping, and that she had metal studs implanted in her knuckles

A good point; it's entirely possible that this is only a very temporary challenger, who will soon be challenged again, and be defeated.

There should be an anime adaptation of this story: Sukeban Saru