3girls, armpits, arms_up, bed_sheet, black_one-piece_swimsuit, blush, breasts, collarbone, competition_swimsuit, cover, cover_page, covered_navel, doujin_cover, feet_out_of_frame, groin, idolmaster, idolmaster_shiny_colors, inuzumi_masaki, izumi_mei, large_breasts, looking_at_viewer, lying, mayuzumi_fuyuko, medium_breasts, multiple_girls, on_back, one-piece_swimsuit, pillow, serizawa_asahi, sideboob, small_breasts, straylight_(idolmaster), swimsuit, w