I liked the 2014 anime, so I read the original manga... but at that time, it was still ongoing. Now, years later, I've gone back to read all the rest. Yeah, that's roughly what I'd expected. It also gets nearer to a happy ending than I'd have expected from Lynn Okamoto, which is to say that almost everyone we know dies horribly and irreversibly, but one or two characters will survive the destruction of their bodies in another form.
If you've seen or read Elfen Lied, you'll know what to expect from Lynn Okamoto. If you haven't, don't worry. You'll soon get the idea. The first chapter I read here (ch.159) is almost the most horrifying thing I've ever read. The only thing I can think of that might challenge it would be this manga's previous chapters. Vingulf have captured a nice girl with psychic powers, so they break her spirit by forcing her to commit lots of murder. "These are B-class witches. They have no value to us. Kill them."
Our heroine can kill you quickly (albeit bloodily). If she doesn't, these random victims will melt to death in front of her, in agony from start to finish. The first one takes 135 seconds. Our heroine can't bring herself to finish off the first girl, or the second, or the third.
The next one looks about eight years old.
"Congratulations. You'll be commemorated on this day. That'll be enough. Killing one person is the same as killing a million, don't you think? Right? Murderer-san."
It then gets even worse.
Meanwhile, Ryouta and the girls are going to attack Vingulf. This is a terrible idea, but that's the kind of choice you make when you're going to die in a few days. Someone called Aphrodite knows some secrets, but is reluctant to tell them. Why? "You'd want to die if I told you."
Don't even consider not taking this literally.
There are revelations. Worst Father Ever. We also learn that Vingulf own something called Loki that can eat the world. Again, this is not a figure of speech. We see it eat a city, which in practice means dissolving it, its buildings and every living thing within.
The concluding run of chapters is oddly... well, exciting. It's written and paced like an action climax, with twists and cliffhangers. Our heroes get to be heroic. Sometimes, though, this means letting their bodies liquify into goo. For a while, it almost looks as if things might work out okay, but of course our heroes are about to face a bunch of nightmare options. Would you save the world by letting yourself get eaten?
In the end, it feels right. This series shouldn't have a Disney ending. What's more, from Lynn Okamoto, you'll know that it's perfectly possible that the villains might win. That might even be the likeliest outcome. Extermination of mankind? Yes, that would be one consequence. An ending of apocalyptic horror to ravage your soul with infinite horror and despair? That's the whole point, isn't it? Ultimately, though, it's more optimistic than that... but it's still a fanservice harem story that's exploring the worst kinds of inhumanity.
That human battery, for instance. And she's just a one-panel throwaway under a table...