Lunala is a large Pokémon resembling a skeletal, legless bat. It has a short snout, dark pink eyes with white centers, and a deep blue area on its upper head that shows a constantly changing starscape. A rigid, raised hood wraps around its head in a crescent shape and drapes around its neck as well. The outside of the hood is yellow, while the inner part that curves around Lunala's head is a pattern of deep blue and white streaks. Its torso resembles a ribcage with a slightly curved spike on each shoulder and three spikes extending from the bottom toward its tail. Its massive wings resemble a bat's wings with the skeleton exposed, except that Lunala's wings have a total of seven "finger bones": four running through each wing, one running along the edge to the outermost tip, and two pointing upwards that may act as claws that are more functional. The four "bones" in Lunala's wings are only visible in segments. The skin of Lunala's wings is an iridescent deep blue and a light blue light source appears to glow from behind its ribcage. A large, pale yellow crescent connects the outermost tip of each wing to the next two inner tips, and the remaining two innermost tips are adorned by yellow, four-pointed stars. The bottom of Lunala's tail is also lined by a yellow crescent with a ridge running up the middle of the tail towards the ribcage.
When Lunala enters its Full Moon phase, its third eye—a light red symbol of an eye—appears on its forehead and the starscape turns to streaks of light. The skin of its wings glows a bright, light blue. It spreads its wings wide so that the yellow parts on each wing are arranged in a circle with the outermost points of the four-pointed stars disappearing in the transformation.
Known as the "beast that calls the moon," Lunala has long been honored as an emissary of the moon. This Pokémon constantly absorbs light to convert into energy and can obscure daylight with darkness. When it spreads its wings to absorb light and glitters, it resembles a beautiful night sky. It is said to live in another world, which it returns to when it opens its third eye. Lunala can create Ultra Wormholes to travel to and from Ultra Space. Lunala and its counterpart, Solgaleo, can create Cosmog, which it is said to be the female evolution of. It can also influence a Rockruff's evolution into Lycanroc's Midnight form with lunar energy. 
It could also be based on Itzpapalotl, a skeletal Aztec goddess and star demon, often depicted with bladed bat wings; Camazotz, a Mayan bat god that was associated with the night, death, and sacrifice; Leutogi, a Samoan protector bat goddess; and Pe'a-pe'a-makawalu, an eight-eyed bat that Hawaiian demigod Maui snatched eyes from. This may also be a basis for Lunala's auxiliary eye in Full Moon phase.
Lunala may be a combination of luna (Latin for moon) and ala (Latin for wing).
Lunala's verbal cry in Pokémon Moon, "Mahina-pea", is based on the words mahina (Hawaiian for moon) and ʻōpeʻapeʻa (Hawaiian for bat). In addition, mahina piha is Hawaiian for full moon.