1boy 2020s 2023 alternate_version_available animated_skeleton balls blue_penis blue_testicles blush bondage bottom_sans bound bound_arms bound_legs ectopenis grey_background legs_apart male male_only mellouwana monster nude penis precum sacrum_lacing sans sans_(undertale) simple_background skeleton solid_color_background solo solo_male string submissive submissive_male sweat testicle uke_sans undead undertale undertale_(series) 1boy 2020s 2023 alternate_version_available animated_skeleton blush bondage bottom_sans bound bound_arms bound_legs grey_background legs_apart male male_only mellouwana monster nude sacrum_lacing sans sans_(undertale) simple_background skeleton solid_color_background solo solo_male string submissive submissive_male sweat uke_sans undead undertale undertale_(series)