Renkinjutsushi to Ao no Tomoshibi

Synopsis

A beautiful homunculus left behind by a great alchemist master―Joshua, a young alchemist, travels with a homunculus named Coco. Even though he has no emotions, Coco is the only partner Joshua can trust. Coco pretends to be human to hide his true identity, but for some reason, he hugs Joshua every night with passionate eyes...!? (source: Tokuma Shoten, translated)