Void Ark: Confirmed to be a relic from the War of Magi?

[Fenral]

I wonder if Ferdiad will play a role in the next installment? After reading abit of lore regarding Scatach I know that she has a fortress of shadow (that tower?) and she's involved with Cu Calain and Ferdiad

Final Fantasy has typically depicted Cu Chulainn as seen in the particular episode in which he was turned into a horrifying, shapeless monster. It's an incident that has pretty much nothing to do with the actual legends surrounding him. Cait Sith is an unrelated figure, but also Irish in origin. Since no actual plot seems to be taken from Irish Mythology, I think it's safe to write it off as clever theme-naming at this point. Echidna, however, is Greek, and also just happens to be the one boss from FFIII's World of Darkness that didn't make it into the CT series.

Digging into the Irish mythology some more, Cu Chulainn and Ferdiad were foster brothers trained by the warrior woman Scathach, each with their own unique strengths, sort of like the hypothetical invincible spear and unbreakable shield. Stuff happens, they are of course forced into a duel to the death from which neither can back down from, and it looks like Cu Chulainn defeated Ferdiad by thrusting his spear Gae Bolg into Ferdiad's... Riiiiiiiight. I defy anyone to convince me that that's not a metaphor. (There's a reason people call it the "Gay Bulge.")