Summer Wars (2009): Characters & Voice Actors, Character Analysis, Character Map, and Family Tree

Summer Wars(Official) is a feature-length animated film directed by Mamoru Hosoda, released in 2009.

In this article, we will reflect on the characters and voice actors of Summer Wars while considering their individual charms and stories. What kind of people were the characters in Summer Wars?

Please note that the following text may contain unexpected spoilers.

Summer Wars (2009) Main Characters & Voice Actors List

Name	Age	Voice Actor (English)
Kenji Koiso	17	Michael Sinterniklaas
Natsuki Shinohara	18	Brina Palencia
Sakae Jinnouchi	90 (Deceased)	Pam Dougherty
Kazuma Ikezawa	13	Maxey Whitehead
Wabisuke Jinnouchi	41	J. Michael Tatum
Mansuke Jinnouchi	70	John Swasey
Riichi Jinnouchi	41	Chuck Huber
Tasuke Jinnouchi	45	John Burgmeier
Shota Jinnouchi	21	Mike McFarland

Summer Wars (2009) Character Map and Family Tree

Character Map

Family Tree

You can view a more detailed family tree by clicking “Characters” on the sidebar of the Summer Wars Official Website, and then clicking “Family Tree” in the window that opens.

Summer Wars (2009) Character & Voice Actor Profiles and Analysis

Kenji Koiso | Voice Actor: Michael Sinterniklaas

Basic Information on Kenji Koiso

I love this character!

The protagonist of the story. A second-year high school student (17 years old) belonging to the Physics Club.

He boasts enough mathematical talent to have narrowly missed representing Japan in the Math Olympiad, but his personality is depicted as shy, and he is not particularly good at socializing.

He is asked by Natsuki, the senior he admires, to take on the strange and dreamlike part-time job of “pretending to be her fiancé” and visits the Jinnouchi family home in Ueda City, Nagano Prefecture. While there, he receives a mysterious email with the subject “Solve me” and solves a code consisting of a sequence of 2056 digits. Because of this, he is reported as the hacking criminal who caused massive chaos in the virtual world “OZ”, although in reality, Kenji made a mistake in the decoding, and it was a completely false accusation.

At first, he was only bewildered, but touched by the warmth of the Jinnouchi family and Sakae’s kindness, he decides to stand up against the world crisis.

“Yoroshiku onegaishimasuuuu!” (Please!)

In the final battle with “Love Machine,” Kenji screams “Yoroshiku onegaishimasuuuu!” (Please!) as he presses the Enter key. This was a belated reply to Grandma Sakae’s words: “If I win, I’m counting on you to take care of that girl.”

When I first saw it, I didn’t understand why Kenji screamed that while pressing the Enter key, but after watching it about twice, I saw the structure and understood the meaning.

In the very beginning of the story, he was a bit timid, but perhaps Grandma Sakae’s death made him grow.

On the other hand, since he is saying “Please take care of me (us)” regarding a request made in Natsuki’s absence, it could be viewed as a rather selfish story.

It turned out well because they ended up becoming “close,” but if they hadn’t, it would have been a rather empty scream. Well, he is the “protagonist,” so “not ending up well” didn’t happen.

The Problem of Whether Someone Like Kenji Exists – Amazing Day Calculation –

Finally, I would like to think about the reality of the character setting of “Kenji Koiso.”

His superficial characteristics are:

If asked whether such a stereotypical “science guy” exists, at least in my experience, they do. A junior of mine at university was exactly like that. He belonged to the Department of Mathematics, was excellent even among them, and was very thin. I think he was reasonably good at socializing, but it is difficult to judge how he compared to people outside of the “science” field.

And he was a very kind man.

Furthermore, early in the story, Kenji demonstrates the special skill of “guessing the day of the week from the date of birth,” which he says is due to “modulo operation.” It is likely that “Zeller’s congruence” (Zeller’s congruence on Wikipedia) was assumed. If you look at the formula in the link, you will see “mod 7” or “mod 100” written, and this is probably what he calls “modulo operation.” “mod 7” means considering the remainder when divided by 7, and “mod 100” means considering the remainder when divided by 100 (“mod” is an abbreviation for “modulo”).

Actually, there was someone in my university seniors who could do the same thing as Kenji. Listening to that senior’s explanation, he used a method that was a bit more “organic computer-like,” saying that rather than calculating furiously, the shape of the calendar would float in his mind.

No matter how good someone is at mental arithmetic, it is thought impossible to derive the day of the week at that speed using Zeller’s congruence.

It seems reasonable to think that Kenji also “used Zeller’s congruence (modulo operation) for the sake of explanation.”

Natsuki Shinohara | Voice Actor: Brina Palencia

Basic Information on Natsuki Shinohara

I love this character!

The heroine of the story. A third-year high school student (18 years old) belonging to the Kendo Club.

She has a bright and active personality, and possesses bold initiative, such as asking her junior Kenji to “pretend to be her fiancé” and taking him to her parents’ home to celebrate the 90th birthday of her great-grandmother, Sakae.

At the end of the story, in the final battle with the AI “Love Machine,” she challenges it to a game of Hanafuda (flower cards) as a symbol of the Jinnouchi family’s unity. Entrusted with accounts from people all over the world, she achieved a magnificent victory.

Intense “Self-Consciousness” Supporting the Start of the Story

I think the story of Summer Wars centers on topics such as the merits and demerits of AI and “family,” but irrelevant to that, it can be said that what essentially propelled the movie Summer Wars was Natsuki’s excessive “self-consciousness”. It might be okay to call it excessive “self-affirmation.”

First of all, I feel excessive self-consciousness in the fact that she thinks someone will just follow her when she recruits for a “part-time job to go on a trip with me,” and I also feel something excessive in the fact that she thinks the retroactive condition of “actually, pretending to be a fiancé is included” will be accepted.

Kenji might have thought of it as a “dreamlike summer trip with the admired Natsuki-senpai,” but from the outside, he is being completely underestimated.

In the first place, it is also strange that she calls out to Kenji and his friend Sakuma. They belong to the “Physics Club,” but on the club room door, the words “PC Club” and the crossed-out words “Otaku Club” could be seen. At the very least, the people in that room are not the school’s “first string.” In short, it means she thought, “These guys would go along with it.“

Thanks to the incident caused by “Love Machine,” Kenji was able to hit a walk-off grand slam of becoming “close” with Natsuki, but it is chilling to think if the “Love Machine” incident hadn’t happened. He would likely have left Nagano with his human dignity completely wounded.

It was a story where the result justified the means.

Sakae Jinnouchi | Voice Actor: Pam Dougherty

Basic Information on Sakae Jinnouchi

I love this character!

Natsuki’s great-grandmother and the 16th head of the Jinnouchi family, which dates back to the Sengoku period. She was about to celebrate her 90th birthday.

Being of samurai descent, she is a woman of great backbone. When the chaos of OZ began to affect the real world, she worked hard to bring the situation under control by calling heavyweights in various fields using only a black telephone. Her connections and ability to take action were worthy of being called the pillar of the clan.

Her words, such as “You can do it” and “The worst things are being hungry and being alone,” truly encouraged not only Kenji but many characters from the bottom of their hearts. She was truly the spiritual pillar of the Jinnouchi family.

The Problem of Whether She Really Needed to Make Those Calls

One of the famous scenes in the movie Summer Wars is the scene where she calls her family and heavyweights in various fields on a black telephone when “Love Machine” caused chaos in OZ.

However, from the first time I saw it, I had the not-so-good impression that “she didn’t really need to make those calls.”

It was truly an emergency at that time, and confirming “family safety” is very important, but you shouldn’t contact people who are dealing with the matter at this very moment. Because it’s just a hindrance.

She scolded the person she was calling who said “I was just about to do it,” but they were probably really about to do it, and she didn’t need to call. And by calling, she caused them to waste time.

I like Summer Wars as a whole very much, but I couldn’t wipe away the discomfort regarding this point alone.

However, when I thought about “Why Grandma Sakae provided financial support to Wabisuke,” the appearance of that telephone scene changed completely.

I have summarized my thoughts on this in the following article:

What did you all think of that telephone scene?

Kazuma Ikezawa | Voice Actor: Maxey Whitehead

Basic Information on Kazuma Ikezawa

I love this character!

A 13-year-old boy who is Natsuki’s second cousin. Usually, he tends to be withdrawn and speaks little, but in the world of OZ, he boasts immense popularity as the martial arts champion “King Kazma.”

He learned Shorinji Kempo from his grandfather Mansuke Jinnouchi to overcome bullying (this experience is utilized in the activities of “King Kazma”). He challenges “Love Machine,” who brought chaos to OZ, and although he is defeated once, he challenges it to a revenge match with the support of Kenji and the Jinnouchi family, but… due to the foolish actions of Shota Jinnouchi, he is defeated again.

Even so, in the final stages of the story, he supported Kenji and Wabisuke and contributed to the victory of the Jinnouchi family.

Wabisuke Jinnouchi | Voice Actor: J. Michael Tatum

Basic Information on Wabisuke Jinnouchi

I love this character!

The illegitimate child of Sakae’s husband, who was adopted into the Jinnouchi family in his childhood. He is Natsuki’s first love and is 41 years old. By blood, he belongs to Natsuki’s grandfather’s generation (meaning he is her great-uncle), but age-wise he is of the parent generation, and Natsuki also calls him “Uncle Wabisuke.”

He was thought to have disappeared after taking the Jinnouchi family fortune, but he wanders back after 10 years for Sakae’s 90th birthday. He has a blunt and cynical side and talks lightly to Grandma Sakae, but he holds deep affection for her.

The AI “Love Machine” he developed becomes the root cause of this incident, but the “fortune he took out” utilized for that research was actually supported by Grandma Sakae.

He took the stance that “I am just the developer of the AI and have no responsibility for this matter,” but after Grandma Sakae’s death, he feels responsible for the situation he caused and ultimately dedicates himself to saving the world as a member of the Jinnouchi family.

The Mystery of Why Grandma Sakae Supported Wabisuke

As mentioned above, the funds for Wabisuke to develop the AI “Love Machine” were supported by Grandma Sakae. However, the problem is that this fact was concealed from the family, and it was made out that Wabisuke ran off with the money.

Watching the movie, it seems the family would have accepted it if Grandma Sakae said she would support him. Yet, she had to hide that fact, and she provided financial support even though she had to hide it.

I have summarized my personal thoughts on this in the following article:

How do you all think about Grandma Sakae’s funding of Wabisuke?

Mansuke Jinnouchi | Voice Actor: John Swasey

Basic Information on Mansuke Jinnouchi

I love this character!

Sakae’s second son, who works as a fisherman in Niigata. He is also Kazuma’s Shorinji Kempo master. He has a hearty personality and could be called a leader who brings together the men of the Jinnouchi family, but he seems to appear as a frivolous person to the women.

Riichi Jinnouchi | Voice Actor: Chuck Huber

Basic Information on Riichi Jinnouchi

I love this character!

He belongs to a “place he can’t really say” in the Japan Ground Self-Defense Force. In the main story, he “borrowed” equipment for satellite communication from the Self-Defense Forces.

Tasuke Jinnouchi | Voice Actor: John Burgmeier

Basic Information on Tasuke Jinnouchi

I love this character!

The owner of an electronics store in town, he “borrowed” a supercomputer scheduled for delivery to a university during the revenge match against “Love Machine.”

If the revenge match had ended successfully, he would likely have been the MVP of the operation, but due to the foolish actions of his eldest son, Shota, the supercomputer caused thermal runaway, and he regrettably missed out on being MVP.

Shota Jinnouchi | Voice Actor: Mike McFarland

Basic Information on Shota Jinnouchi

I love this character!

A police officer. He has a strong sense of justice but is somewhat short-tempered and hot-blooded. He mistakenly tries to arrest Kenji as a hacking criminal, but later reconciles and fights together as a member of the Jinnouchi family.

In the middle of the story, during the revenge match against “Love Machine,” he arbitrarily took out the block of ice placed for cooling the supercomputer “to cool Grandma Sakae’s body,” inviting the thermal runaway of the supercomputer.

Ultimately, the Jinnouchi family won against “Love Machine,” so it was fine, but he is a man who almost became a so-called “war criminal.”

However, he is also the only person among the characters in the story who thought to cool Grandma Sakae, who was alone in the midst of the hot summer. He should have said something regarding the movement of the ice, but it is also certain that he is a very kind man.

Other Characters

       
• Takashi Sakuma | Voice Actor: Todd Haberkorn
       
• Kazuo Shinohara | Voice Actor: Bill Jenkins
       
• Yukiko Shinohara | Voice Actor: Lydia Mackay
       
• Mariko Jinnouchi | Voice Actor: Shelley Calene-Black
       
• Rika Jinnouchi | Voice Actor: Cynthia Cranz
       
• Mansaku Jinnouchi | Voice Actor: Barry Yandell
       
• Kiyomi Ikezawa | Voice Actor: Jennifer Seman
       
• Naomi Miwa | Voice Actor: Lydia Mackay
       
• Yorihiko Jinnouchi | Voice Actor: Robert McCollum
       
• Kunihiko Jinnouchi | Voice Actor: Patrick Seitz
       
• Katsuhiko Jinnouchi | Voice Actor: Christopher R. Sabat
       
• Noriko Jinnouchi | Voice Actor: Colleen Clinkenbeard
       
• Yumi Jinnouchi | Voice Actor: Monica Rial
       
• Nana Jinnouchi | Voice Actor: Cherami Leigh
       
• Ryohei Jinnouchi | Voice Actor: Jason Liebrecht
       
• Mao Jinnouchi | Voice Actor: Cherami Leigh
       
• Yuhei Jinnouchi | Voice Actor: Brittney Karbowski
       
• Shingo Jinnouchi | Voice Actor: Alison Viktorin
       
• Kana Jinnouchi | Voice Actor: Tia Ballard