The story takes place in a luxury apartment in Wako, Saitama. A resident of Apt. 301, Shinichi Tonelli is gathering mistakenly scattered keys of his laptop. Another resident of Apt. 302, Jiro Kasuya is watching him through a peep hole. Swallowing his laughter, Jiro enjoys it as his daily hobby. One day, his daughter Akane finds out about his hobby.

Shinichi always gets fired from his part-time job for making mistakes and his current job is a pet store clerk. He was asked to look after a small animal, very rare ero-erodactyl overnight. Shinichi, who actually cannot touch animals asks his close female friend Sotoko (Emma Miyazawa) for help. By the time Sotoko arrives, ero-erodactyl has already disappeared...

Fired from a pet shop, Shinichi practices for interviews over and over. However, he makes so many mistakes and misunderstandings that it is highly unlikely that he lands a job. Watching this, Jiro decides to disguise as a pizza delivery person to help Shinichi by correcting his mistakes.

Shinichi starts dating with Sotoko and he has her over at his place to play board games. When she goes out for grocery shopping, Shinichi finds and reads a letter that Sotoko was hiding from him. Jiro and Akane, worried that Shinichi and Sotoko's relationship will be shattered, try to hide the fact that Shinichi read her letter secretly.

Akane conceives a plan to make money from live streaming Shinichi as "Tunnelman" through a peep hole. The number of views skyrockets one night. Simultaneously, a famous singer, Let's Dainagon (Goro Inagaki) was spotted in their neighborhood. Disguised as an engineer or technician, he visits Shinichi who is struggling with TV wiring.

Shinichi's mother, Naomi (Mari Natsuki) visits Shinichi from countryside without any notice. Her intention is to convince him to succeed her gas station which she manages by herself. Jiro and Akane tries to stop that because their business of streaming Shinichi was taking off. But things do not go as expected...

As a result of lies to prevent Shinichi from returning to hometown, Akane, Sotoko, and Shinichi end up in a love triangle relationship. Naomi, who now knows about Kasuya family's streaming business gets involved as Shinichi's agent. Moreover, Jiro's wife, who has no clue about this business, suspects that "Tunnelman" is her neighbor Shinichi.

Finally, Shinichi finds out that Jiro and Akane have been spying him through a peep hole. He panics once but soon realizes that he is loved by people worldwide and decides to continue as Tunnelman. However, naturally clumsy Shinichi cannot pretend or act now knowing the truth and it seems difficult to continue the streaming business...