Protagonist have met an accident in the mountain. In the place which started dying, it is helped by the getting lost Elf, the life is saved. When you offer the expression of gratitud to the person, she does an unthinkable proposal.

(When this hideout is known to other human beings i am troubled. I cannot let you out from here, i have you to live together with me...)

Thus, the lewd sweet life with Yumina was started.