seppatsumaru, believe (umamusume), highres, 1girl, ahoge, animal ears, black one-piece swimsuit, breasts, brown eyes, collarbone, covered navel, grey hair, happy birthday, highleg, highleg one-piece swimsuit, horse ears, horse girl, horse tail, looking at viewer, multicolored hair, one-piece swimsuit, red eyes, simple background, singel ear cover, small breasts, solo, streaked hair, swimsuit, tail, white background