Can you do that if somehow you went undefeated by any monster (or did other stuffs) Oniku or rumia comes to your house in the night.
Conditions might be:
1: Sleeping undressed
2: Weird mood on
3: Having high lust or lewdness
High lewdness might bring Oniku in, while high lust might get the other girl in...
Think of it as an Easter egg or a new way to Teach about those 2 stuffs for the people that either are too lucky/pro at fighting or Just mine and search loots everywhere.