An apparently nice family had a Reimyu. She avoided going out when Marisa want to teach her to hunt (they actually live in prosperous place). She grow into a lazybum that only eat from her parents.
Then, when she grew to an adult, her parents asked her to leave the house (she's already in the stage where yukkuri starts wanting to leave their parents' house to start their own life) because if she stay at home, she can continue having free meal.
Mother Reimu is getting angry, both disowned each others. After that, Reimu did house declaration and kill her own mother. She also threatened her own father to get the fuck out of her easy place. It's almost winter by that time.
All of that is a story told by Reimu, so she told Marisa that they have to take good care of their little one.
Wait, so it was basically a Cautionary Tale told by mother Reimu about not spoiling their kid? That's quite a good way to warn her partner of the dangers of spoiling their lil one, it shows she has some serious mother skills.
It's a valid lesson considering we are talking about yukkuris.
Father Marisa: So something like that happens no ze...
Mother Reimu: That's why we have to let our little one take it easy as much as possible.
Father Marisa: It'll definitely grow up to be a yukkuri that can really take it easy no ze.
Mother Reimu: Let's take it easy with mommy little one.
Reimyu: Eajy! Eajy!