The story revolves around Miyagawa Atsushi and his sister Miyagawa Atsumi. Atsushi looks like an adult at 180 centimeters (about 71 inches) tall, but he is actually an elementary school boy. Atsumi looks like a little girl at 137 centimeters (54 inches) tall, but she is actually in high school. (ANN)
As Atsushi prepares for a recorder exam, his appearance to others leads him into a tough situation when he tries to talk to one of his classmates.
Atsumi takes Atsushi shopping with her.
Sayo and Atsumi discuss what kind of guys they like.
Atsushi's elementary school teacher, Futami Moriyama, has problems dealing with Atsushi. Later, being with Hina, Atsushi has a run-in with authorities again.
Atsushi receives a lot of chocolate from the other girls on Valentine's Day.
Atsushi is invited to Hina's house for Hinamatsuri, but is turned away by her suspicious parents.
Sayo goes to the movies with Atsumi and Atsushi, unaware that Atsushi is Atsumi's little brother.
Atsushi and Atsumi's neighbour, Take, comes over after breaking up with his girlfriend and quitting his job.
Atsushi gets help from Atsumi to make some gifts for White Day.
Atsushi tries to do his homework at the library, where he encounters Sayo again.
Atsushi faces yet more misunderstandings with the police.
As people gather for a flower viewing party, Atsushi and Atsumi deal with a drunken Futami
As a new school year starts, both Atsushi and Atsumi face misunderstandings with the new batch of students.
Atsushi's friends try to teach him how to ride a bike without training wheels.
Atsushi and Atsumi think about what they want to do in the future.
As Atsumi ends up making too many snacks for Atsushi and his friends, she invites over Sayo, who continues to misunderstand who Atsushi really is.
Atsushi, Atsumi and their family go to a hot spring inn where Atsumi's height becomes a bother for her.
Atsumi has to act as Atsushi's parent so he can participate in his school's sports festival.
Atsushi and Atsumi have lunch with Sayo before participating in a relay race.
Sayo learns the truth that Atsushi is Atsumi's little brother.
Atsushi wears some clothes handed down from Take, which prove to be a bit controversial.
Atsushi and his friends go to Atsumi's school culture festival where he runs into Sayo.
Atsumi and Sayo spend some time together
A game of hide and seek soon turns into a frantic escape from the cops for Atsushi.