Shoujo Tantei Rinn-chan no Jikenbo - Dennou Shoujo Densetsu

Medieval fantasy world. Sister Norico accidentally got a curse item and turned into an evil witch. Rinn-chan learned the secrets of sex from a mysterious Chinese person, got a special sword of the fox from an alchemist of Central Europe and set to challenge Noriko's demonic dungeon.

[From vndbreview]