I Picked Up a Wishful Mermaid.

I will teach you sex.

[A host lured by his past love] ｘ [A mermaid brimming with curiosity]

Nina admires the world of humans. She took a drug that changed her tail into legs and went ashore to live on land, where she learned the ways of man, but there was nobody to teach her all about sex. What exactly is this act that humans indulge in, if it's not solely for reproductive purposes?

The endlessly curious Nina was rescued in the forest by a man, who she then asks to teach her. Whereupon, the way he uses his hands makes her body feel like it's going to melt...!?

(Source: Fusion Product Comics)