I've been playing the game a lot lately and was wondering how accurate it is. I don't believe a solo ninja was able to take down the Mongols but maybe there were gorilla fighters (some farmers and Ronin) who joined up together?
I'd suggest using the search function and search for the title of the game, and for "Mongol Invasions" :)
But to give a starting point:
The most recent post I'm aware of is this (where I myself gave a summarized reply), which should guide you to multiple other answers.
[for mods: if it would be preferrable to insert every single link separately all over again, I'll gladly do so, but currently reddit - for some reason - bugs out and simply deletes the entire browser tab when I try to to link to them o_O]