The second costume of Pochimaru, as seen in post #4344286, which she used until she debuted her next default.
She retains the long grey hair, flat chest, head wings and tentacles of her original design, but now the wings are attached directly to her head while her tentacles become part of her own hairstyle. It consists of a sleeveless, short black dress with a pelvic curtain, black detached sleeves, aqua shorts and black footwear.
This tag implicates pochimaru_(vtuber) (learn more).