Short synopsis: koMarisa and its parents got into an argument over some petty matters, and it decided to abandon its home in search of a different, "better" family. On its journey, it came across a rapist Alice which took it in, but at the price of constantly raping it and forcing it to eat its own unborn babies. After some time, the koMarisa got fed up with this, and left the Alice. It thought that the life of a yukkuri was no good, and if it (somehow) had became a human kid, then it would've been able to enjoy the easiness that humans have hoarded up for themselves. So, it decided to stop being a yukkuri, went up to a random human and declared that it would become the person's own (human) child.
(alright, just wait a bit for me to recover from a brain hemorrhage and malignant tumor caused by the sheer stupidity of this Marisa's declaration. Had some Suiso facial expressions been added to this thing, I'm afraid I wouldd have punched my screen in irritation)
Ok so back to the synopsis. The human in question -a kid enjoying some fireworks- obviously responded to the dumb shit koMarisa with violence, which included forcing it to swallow the sparks emitted by his firework sticks; it's life was spared though. After all of this, the koMarisa realized that its own family was the most precious family it could've had, and made its way back, only to realize that its parents had capitalized on the fact that it abandoned its family to have more kids, and kicked it out, refusing to accept its return.