1girl, o, ahoge, arisugawa_natsuha, bikini, blush, breasts, cleavage, groin, halterneck, idolmaster, idolmaster_shiny_colors, keshi_kado, large_breasts, long_hair, looking_at_viewer, lying, navel, o-ring, o-ring_bikini, on_back, orange_hair, outdoors, partially_submerged, shading_eyes, solo, sweatdrop, swimsuit, very_long_hair, white_bikini