Hi lonerwolfnanz!
Wow, thanks for playing C:DoD, KAIROS and OFAF! Really happy to know that the world of Gaia is familiar to you, and I hope this visual novel gives it a bit more depth.
* SPOILERS AHEAD *
Have you played Lithiel's route already? If you have, then Lithiel isn't the Keeper of the Memoria; in the Sky Realm, Chronos and Kairos are the only ones who could access it. There is a copy of the Memoria in the Sky Realm and another one in Gaia, which is kept by the Keeper tribe (not mentioned in OFAF).
There are no clear-cut references of Siena and Kain in OFAF, but there is an obvious one at the end of Lithiel's route, where you see young prince Terevska (if you've played C:DoD, Terevska is Ning Jun's old name). Also, if you've talked to the strange cloaked man in Hosheira Desert (Sol's route), he's actually one of Noir's colleagues (from C:DoD)! And don't worry, there's no way your question is offensive. I love answer questions regarding lore, hehe.
Thanks for playing OFAF once again, and good luck with your endeavours too :D