One evening, the silence is broken by Mrs Mitsuba, who is badgering Kenichi to become independent now that Mr Mitsuba is off on a golfing holiday. She then rattles on that Mr Koike told her that Kenichi is being petted too much at school, and sweats as she finishes that she doesn't know what her son will amount to. Upon hearing this, Kenichi furiously declares that he will live independently - however, when he expects Hattori to try and stop him, he congratulates him and decides to live with him. Shinzo and Shishimaru join.
As they walk into the forest, carrying their rucksacks along with them, Hattori finds a Ninja treehouse. He guides them up the rope ladder and shows them the built-in furniture.
That evening, Kenichi has a steambath with Hattori lighting the fire using a piece of bamboo. Kenichi paddles in the giant barrel and says that there's no Mrs Mitsuba to boss him around. After that, they eat their dinner - bamboo-steamed rice. As they engage in light banter, they don't see the events of the following day coming...
Next morning, Kenichi goes back to school, meets Yumeko and Kemumaki, and tells them about his adventure. As Yumeko fawns over Kenichi, Kemumaki brews a nasty plan for Kenichi.
That evening, the gang eat rice made from the root of a tree. Hattori explains the difference between bamboo rice and tree-root rice, and goes on to tell them many more things that can make rice nutritious. Meanwhile in the vicinity, Kemumaki and Kagechiyo prepare blue, red and yellow aroma bombs: the blue bombs smell of curry, the red ones of cooked eel, and the yellow ones harbour the smell of chocolate rolls. As Kenichi, Shinzo and Shishimaru are seduced by the aromas and run off. Hattori freezes them and fans the smells away, much to Kemumaki's annoyance.
Later on in the night, Hattori goes to fetch some firewood. As Kenichi does his homework, Kemumaki and Kagechiyo sneak into the tree house, freeze Kenichi and make him look like he's turned sixty. As Kenichi wakes up, Kemumaki, disguised as an elderly man himself, tells Kenichi that his mother has been waiting for him for fifty years. Horrified, Kenichi dashes back to his home, but he's too late - just as he is reunited with ninety-something-year-old Mrs Mitsuba (who, in reality, is Kemumaki) she collapses of an apparent heart attack.
Meanwhile, Hattori returns to the treehouse, tells Shinzo and Shishimaru of for sleeping on the job, and dashes off to the Mitsuba family's house. He unveils Kemumaki's disguise, numbs his muscles, and he and Kagechiyo wobble home. Kagechiyo quips that it'll take them fifty years for them to get back to their flat.
Next morning, Kenichi camps out in a tent in the garden of the house. After a playful argument with Mrs Mitsuba about mirror TV, Hattori points out that Kenichi will never change.
Mr Koike (mentioned)