The 4th costume of hololive's Himemori Luna, as seen in post #5536694 and post #5772810.
It consists a white frilled strapless dress with a high-low cut with multiple large bows on the chest and the waist and a huge bow on the back, an optional white shawl, white armbands and gloves, white thighhighs and black strappy heels. She also wears a pearl necklace decorated with a crescent and 2 stars and crescent earrings.
She has 3 official hairstyles with this outfit:
Her hair also has a mode noticeable blue gradient, as opposed to the more subtle purple gradient from her precious outfits.
This tag implicates himemori_luna (learn more).