Since it took four years to reach Finnish theaters, I'm guessing this is one of those situations where the pandemic just gave new life to a movie which would have otherwise.not received much in the way of distribution.
The setup is that mankind has been immortal for a long time, but at the expense of our capability to reprocreate. When a pandemic starts to kill people en masse, there is a sudden need to replenish the population, so our hero is sent underground, among the marigan to find the one creature they could identify as having genitalia.
The marigan have been living apart from humans for a very long time and have built their society, although many of them are "wild". They don't follow the usual patterns of species, but will instead evolve in wildlly different ways.
This is the world into which our hero is plunged. He loses his body immediately and his head is placed into a robotic body, which brings its own set of difficulties.
The plot is just bad. Things just happen until the movie just ends. It almost feels like the director just didn't have the time or motivation to make the third act for the film.
Despite this, I did enjoy it. The weirdness of the world does carry the film pretty far. The monster design does remind me of something, but I'm not sure of what. Maybe some demonic beings from Hellblazer or something.
The world is claustrophobic and unfamiliar. Dangers seem to lurk everywhere, but at the same time some people have been living there for hundreds of years, so you can apparently get accustomed to it. While the world certainly is artificial, it also seems to grow like some sort of a living being. No-one seems to have any idea about how big it actually is or how things actually work. Certain people just have found themselves working on jobs, even though they might not really know why those jobs are even there.
So, all in all, if you are one of those people who want a cohesive story, this is not for you, but if you visuals and the art of stop-motion animation are your thing, this is worth checking out.