Winter is closing and a family of Remilia is starving. Recently there's an extermination in the mountain so the family doesn't have anything left to eat.
Mother Remilia is prepared to sacrifice herself, asking her children to eat her when she died. But her children refused.
That night, sleeping hungry dreaming of pudding, the babies are infected with a disease. Their filling turns into pudding (maybe like the system that turns yukkuri into sweets with abuse) and smelling that, mother Remilia lost herself and ate the four pudding.
Still not fully recovered, she approached a new clan and ends up defeated because she's still too weak. But the clan itself is also on the brink of extinction.
The clan then used Remilia as their food stock, taking advantage of her regeneration ability.
But consuming Remilia had weird side effect. The yukkury falls into an orgy and had weird babies. But nobody realized something is wrong.