@Darklight99 @xyzzy @Nabusco
It's an extremely obscure reference to an anecdote or legend during the Warring States period. I've only ever seen it referenced in
either Basilisk or Yagyu Ninja Scrolls. It was in Yama Fu Tang
I don't remember the specifics but there was a lord who only enjoyed men. Uesugi Kagekatsu, became infatuated with a junior samurai and bedded him, before that samurai disappeared for a year.
The samurai then reappeared carrying a child, claiming it was the retainer's. When asked how was this possible, the flimsy explanation of "pregnancy via anus through Nirvana" was given. It's more likely it was a kunoichi who disguised herself as a man and seduced the lord.
This was apparently referenced in the "Ouu Eikei Gunki"
Final Edit: The original story mentions of a kunoichi who could enlarge and shrink her breasts at will, making the Tawawa reference adding another layer with how the one here made her's bigger.
Somewhat related to this guy who pretended to be a woman in order to spy on a French official
https://en.wikipedia.org/wiki/Shi_Pei_Pu