It starts at the dinner table, when the family is eating doughnuts. Shinzo finishes his doughnut, but then wants some more. Kanzo Hattori, seeing Shinzo's desire, divides his doughnut in half and gives one half to his brother. Mrs Mitsuba comments that Shinzo is lucky to have such a brother. Kenichi's face contorts in puzzlement.
Later on, the gang are watching a television programme about an a boy and his little brother. Upon seeing the boy's kindness to his brother, Kenichi turns the TV off and hurries to his room. Shinzo and Shishimaru are outraged, but Hattori is thoughtful. Upstairs, Kenichi wonders what it is like to have an older brother, and wishes that he had one.
A few days later, Hattori gathers the Mitsuba couple, Shinzo, Shishimaru and Kemumaki at the living room of the house for a meeting. Hattori says that Kenichi has been having a bit of a problem. The gathering is curious, but Hattori patiently says that Kenichi has been wishing for an older brother. After Mr Mitsuba and Kemumaki express their views, Hattori says that he wants everyone to help out with this difficult mission. They then get into looking at the old photo albums that are being kept somewhere in Kenichi's room. Hattori says that after they have finished looking at the photos, they will work on the alterations.
Later on, Shinzo takes some artificial eye stickers and pastes them over his own eyes, posing as baby Kenichi. Meanwhile, Mr and Mrs Mitsuba dress into their old clothes. Mr and Mrs Mitsuba state that they're feeling young again. Kemumaki and Kanzo get into the attic, and Hattori supervises Kemumaki's disguise as Kenichi's apparent older brother. Later on, the party goes into the garden to pose for photographs. Hattori proves himself to be a very good photographer. He takes photos of the gang near the garage, then Kemumaki and Shinzo riding on Mr Mitsuba's back. Kemumaki and Shinzo pose for two more photos, before they stop.
Next morning, Kemumaki, disguised as an older boy, goes into the current-timeline Kenichi's room and wakes him up using force. Kenichi tries to get the boy to cut it out, before he looks suspiciously at him. The boy reveals himself to be his older brother, Kentou Mitsuba. Kenichi tries to get the boy to reveal his identity, but he resists. He then complains that Hattori is bothering him in disguise, but Hattori says that he isn't doing anything. "Kentou" then tells Kenichi to get ready for Sunday morning, and Mrs Mitsuba sides with him.
At breakfast, "Kentou" then asks for some more rice, and Mrs Mitsuba tells Kenichi to follow his brother's example. Kenichi then accidentally spills his soup, and Mr and Mrs Mitsuba tell him off. Horrified at his father, too, siding with Kenichi's apparent older brother, Kenichi storms back to his room. The gang express happiness at their success.
In Kenichi's room, Kenichi gets out a photo album and tries to refresh his mind, but finds out that the albums too have evidence that Kenichi has an older brother. Hattori, Kemumaki, Shishimaru and Kemumaki get ready for the ultimate part.
"Kentou" then calls Kenichi to play some catch. Kenichi tries to resist again, and Mrs Mitsuba tells him to listen to his brother. The boys then go out, where a few townspeople see them. They say that Kenichi is lucky to have such a good older brother. Kenichi freezes in horror. Once out of sight, the townspeople reveal themselves as Hattori, Shinzo and Shishimaru. As they scarper off, they meet more townspeople. They make even more compliments about "Kentou". Kenichi grumbles under his breath - and then he finally cracks. He shouts aloud that he has had enough - and then he comes upon Yumeko Kawai. Yumeko wishes him a good morning - but then she goes to talk to Kenichi's brother. Kenichi tries to attract Yumeko's attention, but she says that she didn't notice him. Kenichi finally throws a tantrum that everyone is treating "Kentou" like a role model. Yumeko then takes off her disguise and reveals himself to be Hattori. They then rejoice that their plan has worked, and Hattori freezes Kenichi.
The next morning, Kenichi wakes up to the sound of the vacuum cleaner. Mrs Mitsuba says that Kenichi must be dreaming. Kenichi then celebrates the fact that it was all a dream, and Kanzo Hattori, along with Shinzo and Shishimaru, rejoice that things have gone well.