What engine do the Ys games use?

[ThreeSon]

I assume Falcom has an in-house engine they use for their games, but does it have a name? Is there one engine for the 3D Falcom games and then a separate one for Ys I and II?

[Quint the Alligator Snapper]

There's one engine that was used for Ark/Oath/Origin, which I usually just call the "Napishtim engine", and presumably a different one for I&II. I dunno about the rest.