1girl, ater9, bad_pixiv_id, blue_hair, breasts, bubble, cherry_blossoms, cleavage, collarbone, fins, hair_between_eyes, head_fins, holding, holding_instrument, instrument, long_hair, mermaid, monster_girl, music, navel, night, night_sky, original, outdoors, playing_instrument, reflection, sitting, sky, solo, star_(sky), starry_sky, tree, water