Looking for a Specific Manga

I have been searching all night for a very specific manga. I read it ages ago and cannot remember the name. The basic plot is set in a generic fantasy setting. An Adventuress is in a shop looking for equipment. She spies a sword she likes, but finds it's too expensive to buy. The woman running the shop reveals herself to be a futa, and offers a discount on the sword if the adventuress will have sex with her.

I know it's part of a series, but I can't for the life of me remember the NAME. It's driving me mad.