You have my respect.
I looked through the game's maps/events back in April and didn't find anything resembling a special ending. There could still be some text at least congratulating you on completing the challenge, but now we know there is nothing at all.
I've written on this already in this thread, but the ending is just very bleak, and, to be honest, the game feels unfinished.
I agree it feels a bit unfinished, maybe a future game will help clear things up. They've all lead into each other fairly well so far.
One thought that entered my head after finishing this game was to wonder whether we've been misinterpreting the relationship between the Gravid and the Fuyou. The assumption thus far has been that the Gravid are giving birth to the Fuyou, and that's why they are trying to corrupt the world, to make it produce more EP so that they can have more kids. One thing that struck me, especially after the encounters with the giant eye Fuyou demanding EP from us at the end was that ... what if the Gravid want EP because the Fuyou want EP?
The Fuyou lead to instant game over if you so much as interact with them, to the point that in the first game you find documentation that informs you that they are impossible to kill and the only thing you should do on encountering them is run. Should you fail to run or be surrounded, you are to kill yourself.
This is not however how the Gravid interact with us. The Gravid want sexy times with us, and clearly are something that we can interact with for a long period of time, during which we generate EP, without dying.
So what if the Gravid are a life-form that is kind of a middle stage, a life that requires EP like the Fuyou, but isn't so fundamentally and incomprehensibly alien to our existence that we are basically instantly unmade and incapable of recovering if we interact with them. Because in game, we can die all we like in the EP world normally. We can drown, get crushed by metal cylinders, fall from a great height, and all that happens is our unconscious body wakes up back outside that particular pocket dimension. But even with that ability to survive seemingly any sort of death, the Fuyou trump that, and just instantly unmake us. Perhaps they simply pull us apart into EP, energy from mass.
Maybe the Gravid are some sort of middle state, where they can still interact with us, and use us for EP generation in a more benign manner, rather than unmaking us into EP on contact. And maybe that middle stage means that they can also interact with the Fuyou without being unmade themselves. So what if instead of the Gravid giving birth to the Fuyou, the Gravid are instead trying to gather enough EP to both sustain themselves and keep the Fuyou fed, because the Fuyou don't eat sustainability, unlike the Gravid. The Gravid can corrupt a world, and that world and it's populous will continue to generate EP which they can then use. The Fuyou on the other hand just unmake what they touch, which then leaves the Gravid in the position of being hungry again too, because they both normally get their EP from the same source, which the Fuyou have now unmade.
This leaves the Gravid trying to corrupt more worlds quickly enough to sustain themselves, and still have leftovers to give the Fuyou to sustain them, so they don't go hunting down worlds on their own and leaving the Gravid with nothing to eat again.
I have no idea what anyone else will think of this, but these were the thoughts that came to me at 3 AM while I was playing last night and I felt like sharing my ramblings. I don't think there is anything actually in the games that supports this wild hypothesis, but I don't remember seeing anything that contradicts it directly either. I might have just forgotten though.