The 4th costume of hololive English's Nanashi Mumei, as seen in Danbooru post #7259920. It has an emo motif (translated into Japanese as punk rock).
It consists of a black lace-trimmed choker with a heart pendant, a black print t-shirt featuring a variation of her infamous "Nightmare" painting with a torn black and red striped sweater underneath, giving her short over long sleeves, an owl necklace, a black pleated skirt half miniskirt with a black belt, an o-ring thigh strap, uneven mismatched legwear (a single black fishnet kneehigh with a white leg warmer on her right leg and a black leg warmer on her left, both depicting her mascot Friend) and black platform boots.
Her official hairstyle with this costume is long hair in either twintails with sidelocks or a one side up. Both styles are tied with black hair ribbons. She also sports long asymmetrical bangs over her right eye and a huge ahoge.