Incredible game. Just finished the full thing, with my final save clocking in at about 23 and a half hours. I hadn't the remotest idea it would be any considerable length at all when I downloaded it for free, let alone as long as a triple A game.
In terms of review I have quite a bit to say. I selected normal difficulty at the start, then promptly forgot I was given a choice, and spent most of the game thinking it was too easy. However even on normal I found Hell to be quite a challenge, and an enjoyable one at that. I'll likely revisit this game eventually and replay it on a higher difficulty; it deserves that. I beat Cephiti but absolutely could not beat the other boss in the area, so the balancing there might be a bit off, as you said Cephiti wasn't even meant to be beaten at all.
I love the writing in this game. You have a definite voice and it permeates the entire thing. Initially I wasn't a fan of how prominent it was causing it to affect the tone (though I didn't hold it against you, that tends to happen with indie games) but by the end it had fully won me over and I think the game overall is better for it. I do think the lighthearted and parodical tone of the game led to some of the big emotional beats, climactic moments, and plot twists feeling a bit more hollow than was probably intended, but honestly just playing around with the sounds, music, and pacing of those moments could probably fix every problem in that area. I'm also not a big fan of mysteries where the answer is "whatever you think the answer was" like some of the stuff in the ending looks to be, but the game was very good regardless. I hope Ellicide (I think that's the daughter's name?) returns in something in the future, since as far as I can surmise all Makyo-related content is non-canon. I'm not sure if all the meta talk and timeline reset is diegetic (my brain is poisoned from Undertale) or just a fun framing device to work Makyo in, but if it is diegetic I find it very compelling. Especially whoever it was asking me if I was satisfied with the game.
Oh, and the translation machine can go pound sand! I figured out both the codes on my own to the point that I could pretty reliably read any weird message I found. To be fair it usually took me a while to translate it out in my head, but I got to the point with one of them that some sentences I was reading like plain text. I think you should put some one-off dialogue in somewhere that's a mix of both codes just to throw any others like me for a loop. (This might not be possible, or it might already exist and I missed it.)
Anyway, lot of rambling to say amazing game and I'm definitely going to play more of your catalogue eventually.