Known lore bits on Sui-No-Sato? + more questions

[Botandoro]

Raen actually are shown to live in several nations so far.

They're one of the major races in Thavnair (a location mentioned many times throughout the story and finally visited in Endwalker) and also some amount of population in western Ilsabard around Werlyt and Terncliff, visited in the level 80 trials questline.

They generally seem to adopt whatever the local culture and naming conventions are.

Definitely will be looking into Thavnair as i entirely forgot about it, to be honest. If anyone has links to read up on its lore, I'd appreciate it! Been doing a lot of the side quests in the area today, but still feels like I'm missing a lot.

[Cleretic]

Definitely will be looking into Thavnair as i entirely forgot about it, to be honest. If anyone has links to read up on its lore, I'd appreciate it! Been doing a lot of the side quests in the area today, but still feels like I'm missing a lot.

Honestly, if you're unsure about a region that's actually in-game but have no specific questions, I recommend doing every single quest. Like, top-to-bottom, whole thing. You never know which corner of it all will spark some inspiration. The Encyclopedia Eorzea 3's got plenty on it too, but very little of it is stuff you can't glean elsewhere.

You seem to be orbiting around the concept of putting the character somewhere adjacent to the region's religion, and that one could be genuinely really interesting with Thavnair. Because their faith and mythology actually is a pretty center-stage part of their story, but also doesn't seem to be a particularly big part of their lives. Yeah, they believe in the Mrga and Manusya, we hear a few teachings, there's religious sites about the place and there's some minor mentions of monks and pilgrimages in places like the fishing log, and it's definitely still a present-day part of their lives from the events in the MSQ, but we never meet anyone who's serious about it, a genuine person of the faith. That gives you a lot of potential canvas space to paint in, and maybe that absence is itself something you could find some story hooks in; just as an example, maybe a monk who's facing a crisis of faith after the Magus Sisters and Asura situations, or in entirely the other direction, someone who thinks that after everything that just happened to Thavnair, maybe the religion they've been neglecting has some useful things to teach them in this new and weird era they've found themselves in.

EDIT: Honestly, if you're serious about making a religious character, your best angle might be to study the real-world religion(s) that inspired the fictional one. Thavnair's religion is Fantasy Hinduism, so any gaps about the faith itself should rightly be filled in by Hinduism, as that's what the writers would do. You make a character of the Halonic Church in Ishgard, you're borrowing from Catholicism. Far Eastern kami worship is largely borrowing from modern Shintoism; Gridania's put a western fae coat of paint on more historic and traditionalist Shintoism.