Oninaki Wiki

A Marine Penmy is a Fallen in Oninaki.

Fallen that resemble seabirds. Not very strong on their own, but they make up for it by moving in flocks. Watch out for their chained beak attacks.
Research Log 1-2
After sedating and examining the Penmy, I discovered something incredible: they feel wonderful to pet. Most notably, the dark blue areas of the ones adapted to water are smooth enough to rival the finest silks.