A pair of wild Marisa and Reimu came to a human's farm.
While being beaten, they begged to be let alive because the little ones are innocent and really easy.
To prove that, the man taped their mouth and bury most of their body to the ground. Their head are cut open to give nutrients (soil and grass).
He want to try the baby, a single surviving Marisa from the stalk.
Wearing Marisa's hat, he gave grasses for the baby to eat.
Using Reimu's ribbon, he cleaned up the shit Marisa made and hit Marisa for messing her own house. Marisa one day found out that she doesn't get beaten if she shit on the mound at the corner of the house (her parents' head) so she starts doing it.
The human never talk to Marisa. He only bring food and clean the shit, nothing more. Marisa is so lonely, one day she starts shitting in the middle of the house just to get attention. But after a few days, the man gave up, stare coldly and just clean the shit.
After Marisa grow into koyukkuri, he opened the plastic house a bit, showing Marisa his farm.
Like a yukkuri, Marisa think the farm is her easy place and this human is stupid.
That prooves it. Even without influence from the parents, this is yukkuri. He grip crushed Marisa and then throw both parents to the same wooden box as their child.