"
Monster Musume no Iru Nichijou", a popular ecchi manga that features
a harem of monster girls, has a slime girl and a plant girl that can grow into
adult forms casually from time to time.
Slime girl, named
Suu, can grow into a mature form upon absorbing water (
Ability first shown in chapter 9):
Plant girl, named
Kii, can grow into a mature form upon absorbing nutrients and water from soil (
Ability first shown in chapter 20):