Hi! I’ve been working on a list of RPGs (mostly japanese or j-influenced somewhat) in which the cast is mostly adults. The list is hosted on backloggd.
Leaving it here both in case it may be useful to anyone, but also in case you spot any missing titles that you believe should be added :) cheers!
P.S: the only reason for not taking western RPGs into consideration is because… well, most of them already feature adult casts. Think series such as Divinity, Shadowrun, Baldur’s Gate, etc. However, those usually play dramatically different when compared to the JRPG-style turn-based combat.
Looking through the JRPGs I own, most of them with adult cast are western made. Depending on how far you go with j-influenced some might fit on your list. Zeboyd games is a western studio making JRPG like games with their own twist on them. Cosmic Star Heroine have a completely adult cast. Been years since I played through the Cthulhu games, but I remember the cast being mostly adults in them.
CrossCode from Radical Fish Games stretches what I consider a JRPG to be, but it still comes up in my library when searching for the tag. I think most of the cast were young adults rather than children.
Fell Seal: Arbiter’s Mark by 6 Eyes Studio is pretty much a Final Fantasy Tactics.