Galatea likely never, Helius described her in lore as a child, something few if any distributors will touch and Steam has a parity policy so it's moot anyway if he finds one who'd take it. The game would need to come off steam first since the last time he posted something about discussing her with steam it was going fairly poorly, they're just outright refusing with no negotiation. He seems to be rushing Yanshi as a next character to get a loli in, see how that goes since he's described her as a slightly older Galatea, which probably won't help his chances on steam.
As for Celia, was supposed to be stage 2 of the beta or something, but with the delay that's all out of wack. So who knows really, whenever they get around to it. I think she was meant to be the final free girl before passes, though knowing Helius that'll probably change.
