I only know the OVA (and I can't find anything written about the original game), so that's all I'd have to go off of.

To be fair, I know basically nothing about it either.

But I still think it's funny that "Long ago, there was a battle between humans and monsters, and the humans were victorious and sealed the monsters under the mountains with a magic spell" is literally the plot of both Mouryou no Nie and Undertale.

The OVA irks me a bit. Ep2 reusing some footage from ep1 again, and while ItA omits Takeru, the Mouryou OVA omits like 80% of the roster lol. It's got a bunch of characters not in the OVA at all, along with the awesomely gross bug mummy and orc guy.

I tried playing it last year or so again. But the game has a weird non-linear route for its story, and I gave up trying to 100% the game. Which was annoying because I really wanted to see the milf scenes in full.

HOW DO I GET END 1 AND 3???   It's like this graph should make finding the endings easier, but it wasn't the case. Older TB games were so dense, it's hard to 100% them raw. lol

I forget if it's 100% official, but I think we can pretty much assume Inyouchuu and Mouryou are in the same universe. Similar themes and as I always joke, Mouryou is more hardcore than Etsu.