Futa Potion

The Futa Potion is a gender changing potion that's quite special since it can be used to enable certain gallery entries if given to certain NPCs, currently Mya and Lumira.

Acquisition
Castalia's 3rd quest objective of getting 100 points through submitting sufficient new species/hybrids (gives 1).

Rose's unique encounter event, as long as you accept her into your party (gives 1).