Ayayaya world is one particularly cruel, less abyuse and more humanity doesn't give a fuck about Yukkuri. I'm trully hyped with those ankos and the Dosu circus. I hope someone can provide a summary.
Let me take a wild guess at the narrative. The human is running a weed wacker through the underbrush and splatters a few yukkuri. Marisa here takes a nasty hit, but not enough to kill her. Paste, ichor, and tissue from other yukkuri get into the wound, maybe a bit of paste core, and we get a parasite twin. "Mister Quaid, start the reactor easy!"
Study_it_easy said: Let me take a wild guess at the narrative. The human is running a weed wacker through the underbrush and splatters a few yukkuri. Marisa here takes a nasty hit, but not enough to kill her. Paste, ichor, and tissue from other yukkuri get into the wound, maybe a bit of paste core, and we get a parasite twin. "Mister Quaid, start the reactor easy!"
Another possibility is that this one of those creepy scenarios of a family member or lover, keeping a "memento" from a long dead beloved one, and Little Marisa is keeping the face othe other Marisa to remind her of her sis/parent/lover.
If it went crazy enough, yup, I think we already had stories of yu's doing like those horror stories of crazy dudes acting like the corpses of their relatives are alive and stuff, so it isn't farfetch'd, the whole point would be the yu is crazy and this whole scenario is creepy...
Never Said that it was this case, just my hypothesis until we get a translation and commenting how it is possible for such creepy scenario to happen since I recall similar creepy behaviour from broken yu's. For all we know this could be an accident of the face flying and getting stuck on the marisa and she being unable to take it off...so many ways to explain this scenario...