At Sanwa Nursery, children who keep their pure hearts intact spend each day joyfully. Today, Mako-chan and Runa-chan are playing with toys, and we sneak a peek at their fun. Mako-chan is deeply absorbed in her toys, but from holding her pee for too long, her bladder is about to burst. Unable to use the toilet properly, Mako-chan ends up wetting her diaper. Seeing this, Teacher Iori kindly helps her change. As Runa-chan watches Mako-chan cuddling with the teacher, she gazes on with a hint of envy.
During singing time, they happily perform a round of "The Frog Song," but everyone is stunned when a wet spot spreads across Runa-chan's pants. Perhaps seeing Mako-chan's diaper change made her jealous—Runa-chan ends up wetting herself so much that a puddle forms beneath her feet. Teacher Iori comes to assist, dressing Runa-chan in the same kind of paper diaper as Mako-chan.
Now both wearing matching diapers, nap time begins. Excited by their diaper twin look, the two can't fall asleep. Holding hands, they joyfully pee into their diapers. They giggle about how cute the bunny patterns on each other's diapers are, then swap wet diapers to make up after a small quarrel. Feeling their friend's warm pee against their crotch, they finally drift off to sleep.
To help them master proper elimination, Teacher Iori conducts a poop training session. Both Mako-chan and Runa-chan struggle, trying hard to push with their stomachs and relax their bottoms. Runa-chan manages to squeeze out a soft little poop. But Mako-chan, suffering from constipation, can't go. Then, after Runa-chan gives her an enema, hard little pellets finally come out.
On another naptime, Runa-chan moans in discomfort. Mako-chan realizes, "Her poop has hardened inside her tummy, that's why she's hurting!" Careful not to wake her, Mako-chan administers an enema. Soon, with loud noises, Runa-chan's poop fills her diaper. Her sleeping face softens into peace, and Mako-chan sighs in relief. The two snuggle close and continue napping.
During one elimination session, Mako-chan accidentally licks Runa-chan's poop. Seeing this, Runa-chan becomes curious about the taste of Mako-chan's poop too. The two decide to try each other's. They give themselves enemas together and happily poop into their diapers at the same time. Not satisfied with just a quick taste, they start playing—kneading the poop like clay, writing their names with it like crayons, and even feeding it mouth-to-mouth, innocently enjoying their poop play.
Suddenly, Teacher Iori appears, furious and scolding them harshly. After spanking their bottoms as punishment, she puts cloth diapers on both girls to prevent them from removing them on their own. Though it's their first time in cloth diapers, they're delighted by the cute patterns. Despite just being punished, the two whisper quietly, making promises to play with poop again—such a heartwarming, mischievous sight.