Elf-san wa Yaserarenai.

Elf-san wa Yaserarenai. (エルフさんは痩せられない. ) is a manga series by Synecdoche. It is serialized in Web Comic Gum. It has been licensed in English as Plus-Sized Elf by Seven Seas Entertainment.

Plot
Naoe-kun, a massage therapist, is about to head home for the day when he's saddled with a rather strange patient. This lovely lady has emerald eyes, pointy ears, and grew up in the forest–everything about her screams “elf,” except for one thing: her bodacious body. It turns out she left her world but loves junk food in this one, and now her obsession has caught up with her. Can Naoe-kun help this loveable elf girl lose the weight–and keep it off?