The Door Into Summer: Explained (Japanese Film)

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The Door Into Summer is a 2021 Japanese romantic science-fiction directed by Takahiro Miki. The plot follows an inventor who is tricked by his girlfriend and business partner to find himself in a bizarre situation where his future will become his past. The film is based on Robert A Heinlein’s novel by the same name. The movie is very tastefully adapted and has a very charming romantic angle. Here’s the plot and ending of The Door Into Summer explained; spoilers ahead.

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Here are links to the key aspects of the movie:

The Door Into Summer: Introduction

Soichiro tricked by Rin

Soichiro Takakura is an intelligent kid with a tragic past. His mother died at birth, and his father at 17. A family then takes him in. His adoptive father is a robotics engineer and teaches Soichiro everything about electronics and robots. Riko, the family’s daughter, eventually falls in love with Soichiro but keeps it to herself. Unfortunately, both his adoptive parents die in a car crash. Riko moves in with her uncle Kazuhito and Soichiro continues on alone, inheriting a portion of his adoptive father’s company Future Works Enterprise (FWE).

Kazuhito gets a third of the company’s shares written in his name as per his brother’s will. Kazuhito plots to take complete control of the company and uses his accounting secretary, Rin Shiraishi, to seduce Soichiro and get another one-third written in her name. Soichiro falls for it and gives her the shares.

The story after this point can be seen from two perspectives – one, from Soichiro’s (as the film shows us), and another, from the rest of the world’s. We’ll go through both perspectives. Also, note that this film has only one timeline and therefore only one set of events between 1995 and 2025. No event in this time period is altered in any way.

The Door Into Summer: Plot Explained: Soichiro’s Perspective

8th March 1995

Kazuhito and Rin are now major share-holders and vote to sell the rights of the robotic designs to a company called Mannix Enterprises and block Soichiro’s access to his own research. An FWE truck seizes everything from Soichiro’s home and drives away. 

Riko shows up and confesses her love to Soichiro, but he tells her she’s only a kid and needs to focus on school.

Soichiro goes to the Cold Sleep office of Credeus but is sent back because he’s drunk.

Kazuhito and Rin meet later to discuss their plans on the Plasma Battery, which Riko overhears and makes a run for Soichiro’s home, and Kazuhito goes after her.

Soichiro shows up at Kazuhito’s and threatens Rin he will go to the media and expose how he was tricked. Rin distracts Soichiro and injects him with some knock-out drug. Pete-cat makes a run for it after scratching Rin.

Soichiro wakes up in a Cold Sleep capsule handled by a subsidiary of Mannix Enterprises. Since Rin helped them evade taxes early on, they do her a favour of independently running Soichiro’s cryo-sleep.

8th March 2025

Door Into Summer 2025 - First Time

Soichiro wakes up after 30 years and is told that Mannix went bankrupt years ago.

Soichiro is coincidentally assigned a humanoid nurse by the name of Pete. We’ll call him Pete-bot.

The officials mention to Soichiro that Riko has been trying to contact him.

Pete-bot, who is apparently self-aware and looks like is the first bot with artificial intelligence, disobeys his instructions and leaves with Soichiro and takes him to the place where the calls from Riko have been coming from.

It turns out Rin has been calling posing as Riko because she knows that’s the only way Soichiro will come. She says it all went to hell once she put Soichiro into Cold Sleep in 1995. Kazuhito died of a diabetic stroke later that year, and a mysterious man with Soichiro’s stock certificates showed up and ruined everything for her. She also says, the night Soichiro went into Cold Sleep, Riko, who went running to Soichiro’s house, went missing after the home exploded.

9th March 2025

Pete-bot, Riko dead

Soichiro and Pete-bot get to Guardian Manufacturing, the company that bought FWE. They meet Gota Tsuboi, the president who is in awe of Soichiro and says he became an inventor because Soichiro inspired him. Gota mentions that Soichiro had given Aladdin (company) exclusive rights decades back, causing Soichiro to be confused as he doesn’t remember any of this. Gota finally mentions that decades back, Soichiro had come to meet Professor Toi, another name Soichiro has never heard of. He explains Toi was a regular customer at his family restaurant and was once arrested for embezzling research funds from the university.

Later, Soichiro sees an old video of Professor Toi claiming that time travel is possible.

10th March 2025

Gota Tsuboi helps Soichiro find that the FWE stocks were assigned to Taro Sato (who later founded Aladdin) by Soichiro in 1995 after he went into Cold Sleep.

Soichiro also discovers that the documents state that the first model, PETE-1, is patented to him; PETE-2 is patented to Riko.

Soichiro can’t remember any of this because it has not happened for him yet.

11th March 2025

Soichiro and Pete-bot meet Professor Toi, who is waiting for them with a time machine. Toi explains that Soichiro has made all this possible through time travel. Toi hands Soichiro some gold bars, which is valueless in 2025, and asks that Soichiro converts them to money in the past and gives it to a younger Toi to fund his time machine research. Toi also urges to complete the design for the Plasma Battery as that is needed for the Time Machine. Toi bootstraps funds for his own research through the power of time travel.

Pete-bot joins Soichiro in the time travel to the past. I’ll refer to them from now as Soichiro* and Pete-bot*. 

28th February 1995

Pete-bot* and Soichiro* are intercepted by a lawyer named Taro Sato, who happens to be driving past. While Soichiro* is unconscious, Pete-bot* proves they are from the future by revealing that he is a robot powered by a Plasma Battery. He fills Taro Sato in with all the details.

Taro’s wife, Midori, once a sports person, is now paraplegic due to a terrible accident and, as a result, has become socially isolated. The arrival of time travellers brings back her old self, and Taro’s decision to help stems from this. When Soichiro* comes to, Taro has already cashed the gold and arranged for a room where Soichiro* can complete his research and invent PETE-1.

1st March 1995

Soichiro* goes to Tsuboi Restaurant and meets Professor Toi. He tells him his concept for time travel eventually works and that he is a time traveller from 2025. Soichiro* hands Toi the money. 

Soichiro* talks to the young Gota Tsuboi at the restaurant and tells him that he will become a great inventor one day.

Soichiro* requests Taro to expose Mannix Enterprises for tax evasion and go after Rin Shiraishi. He asks Taro to patent PETE-1 and the Plasma Battery under a new company (Aladdin). Soichiro* offers Taro the FWE stocks and the presidency of Aladdin in return.

Soichiro* also asks Taro and Midori to adopt Riko.

2nd – 7th March 1995

Soichiro* lays low and works on his PETE-1 prototype and the Plasma Battery and completes it.

8th March 1995

Pete-bot* intercepts the FWE truck with Soichiro’s research and steals it.

Soichiro* goes over to Kazuhito’s house, where he sees his past self assaulted by Rin. Soichiro* grabs Pete-cat and leaves with Soichiro’s truck. 

At Soichiro’s home, Soichiro* meets Riko. Pete-bot* joins them. Soichiro* blows up his house and leaves with Riko and Pete-bot*. Soichiro* tells Riko that he is from the future and needs to return.

Pete-bot* offers to stay with Riko.  

Soichiro* heads to Credeus for the Cold Sleep appointment that Soichiro had taken. Remember, at this point, Soichiro is being forcefully put into Cold Sleep by Rin in a subsidiary of Mannix while Soichiro* is at Credeus.

8th March 2025

Soichiro* wakes up in 2025 and is greeted by Pete-bot* (Pete-cat was in Cold Sleep too). Pete-bot* is the humanoid who waited 30 years. Note that another Pete-bot is just being introduced to Soichiro, who is waking up for the first time from Cold Sleep elsewhere. 

Soichiro* reads a letter from Taro Sato to learn that Riko went on to graduate and eventually invented the PETE-2 model. In 2005, she entered Cold Sleep to wake up and be with Soichiro*. With their age difference sorted, Soichiro* meets and begins his new life with Riko.

The Door Into Summer: Plot Explained: Rest Of The World’s Perspective

27th February 1995

An ordinary day where Soichiro has no idea that the next week will be the longest one of his life.

28th February 1995

There are two Soichiros here – one who has arrived from 30 years in the future (Soichiro*) and the other living his life as an inventor (Soichiro). No one other than Taro and his wife, Midori, knows about Soichiro* and Pete-bot* (the time-travelling android).

1st March 1995

Soichiro is at home watching the news about himself on TV.

Soichiro* is at the Tsuboi Restaurant handing money to Professor Toi and telling Gota Tsuboi that he will be a great inventor one day.

2nd – 7th March 1995

Soichiro works on the A-1 prototype and gets tricked by Rin, who gains ownership of a third of FWE.

Soichiro* works on PETE-1 and the Plasma Battery at Taro’s place and figures the patenting details with Taro.

8th March 1995

Soichiro gets doubled teamed by Kazuhito and Rin and is incapacitated in his own company. His research work is taken away by two men in a truck which is intercepted and stolen by Pete-bot*.

Soichiro gets drunk and goes to Credeus to opt for Cold Sleep and is asked to return the next day because of his high blood alcohol levels. 

Soichiro goes over to Kazuhito’s place to threaten Rin but is subdued by her. Note here that the company truck with the research material hasn’t contacted them yet, and now we know why. 

Pete-cat runs away after scratching Rin. Soichiro* is watching all this from outside the house, takes Pete-cat, and leaves in Soichiro’s truck.

Soichiro* meets Riko and Pete-bot* joins them with the truck. Soichiro* blows up his house and tells Riko that he’s a time traveller from the future and not the guy she met in the morning. 

Taro and his wife plan to adopt Riko. Pete-bot* stays with Riko.

Soichiro is forcefully put into Cold Sleep by Rin at a Mannix subsidiary facility.

Soichiro* and Pete-cat go to Credeus’ Cold Sleep, the appointment created by Soichiro.

Later in 1995

Taro exposes Mannix for tax evasion, and Rin gets jail time.

Taro sets up a company called Aladdin and establishes Soichiro*’s patents in them.

Kazuhito gets sick and dies from a diabetes-related health complication.

Riko resumes school.

1996 – 2004

Mannix goes bankrupt.

Given that both Rin and Kazuhito are out of the picture, Taro is the only active stockholder and sells FWE to Guardian Manufacturing, started by Gota Tsuboi. Taro also authorizes Guardian to use the designs for PETE-1 and the Plasma Battery to conceptualize robots.

Riko also gets into Robotics and eventually works at Guardian to create the PETE-2 model, patented on her name.

Professor Toi builds his time machine but in secret.


Riko goes into Cold Sleep.

2005 – 2024

Guardian Manufacturing’s robots become a reality and begin to power every aspect of society, including hospitals. 

Pete-bot is manufactured and is tasked with the job of a nurse.

Taro, his wife and Pete-bot* wait for Soichoru* and Riko to wake from their Cold Sleep.

8th March 2025

Door into summer 2025 - Second Time

Soichiro wakes up after 30 years in the Mannix subsidiary and meets Pete-bot for the first time. The two meet Rin to learn about a mysterious man who took down Mannix and sent her to jail in 1995.

Soichiro* (and Pete-cat) wakes up after 30 years (his second Cold Sleep) at Credeus and reunites with Pete-bot*, who has waited 30 years.

Riko wakes up after 20 years at Credeus and reunites with Soichiro*, and the two start a new life together.

9th March 2025

Soichiro and Pete-bot meet Gota Tsuboi to learn about the past – Aladdin and Professor Toi.

Soichiro*, Riko and Pete-bot* lay low at Taro’s place, and they don’t want to cause any interference in what Soichiro and Pete-bot are doing.

10th March 2025

Gota Tsuboi helps Soichiro find that the FWE stocks were assigned to Taro Sato by Soichiro in 1995 after he went into Cold Sleep.

Soichiro*, Riko and Pete-bot* lay low at Taro’s place, and they don’t want to cause any interference in what Soichiro and Pete-bot are doing.

11th March 2025

Soichiro and Pete-bot meet Professor Toi and travel back in time.

Soichiro*, Riko and Pete-bot* lay low at Taro’s place, and they don’t want to cause any interference in what Soichiro and Pete-bot are doing.

12th March 2025

Soichiro*, Riko and Pete-bot* Taro and his wife can now resume their lives as a happy family.


There you have it! Both perspectives. What were your thoughts on the plot and ending of The Door Into Summer? Do leave a comment below.