The 5th costume of hololive's Yozora Mel, as seen in post #4073642.
It's a gothic lolita-themed outfit consisting of a white collared frilled sleeveless shirt with a frilled shirt collar and center frills a bat-shaped brooch, a black underbust cross-laced bodice, black frilled detached sleeves, a frilled layered two-tone black and white lowleg miniskirt (although it's almost microskirt in length) with a longer overskirt, uneven black frilled thighhighs with different patterns and black strappy heels with a small bow on the top.
Her official hairstyle with this outfit is long hair tied into a two side up with an ahoge and double-parted bangs held with a large heart hair ornament on one side and a regular hairclip on the other, she also has head wings and her hair has an orange-ish gradient.
This tag implicates yozora_mel (learn more).