The idea of a Luna-inspired tattoo instantly makes me think of celestial beauty and mystery. For a detailed design, I'd blend elements from mythology and astronomy—maybe a crescent moon cradling a tiny, intricate galaxy, or Luna herself as a serene figure draped in starlight. Adding subtle watercolor washes in midnight blues and silvers could give it that dreamy, ethereal vibe.
Another approach could focus on symbolism—pairing the moon with wolves, owls, or even a lone willow tree to echo themes of intuition and cycles. Personal touches like birthstone colors or constellations meaningful to the wearer would make it uniquely theirs. I'd probably doodle rough sketches first, playing with line weights and negative space until it feels just right.