- "Future" is the name of the sister's character in the film, and the director's daughter is also called this name .
- The male protagonist is set as a 4-year-old boy because Mamoru Hosoda's son was only 4 years old when he conceived the story. In his view, age 4 is the age where seriousness meets hedonism .
- Moka Kamishiraishi was supposed to audition for the role of "Future," but ended up as the voice of a 4-year-old boy in the film. To this end, at the age of 18, she went to kindergarten to experience life .
- Since 2017, Mamoru Hosoda has been casting for the important character "Youth" in the story, but it is difficult to find a suitable seiyuu. At the beginning of 2018, Mamoru Hosoda reunited with his friend Masaharu Fukuyama and found that Masaharu Fukuyama fits the character very well, so he asked He dubs the character .
Mirai behind the scenes gags
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Mirai: You did it again. You tried to hit me with your bullet train even after Mom told you not to.
Kun: But it wasn't a bullet train!
Mirai: You aren't supposed to use a bullet train to hit people.
Kun: It was a Super Azusa.
Mirai: [angrily] I don't care what kind it was!
[scoffs]
Mirai: And why can't you be a little nicer to Mom?
Kun: I don't know, I just can't.
Mirai: It's her one day off from work. She doesn't get many and she has to spend it fighting with you. Come on, try.
Kun: [sniffling] I know... I'm not cute.
Mirai: Huh?
Kun: [crying, wipes tear from his eye] Both Baby Mirai and Yukio are really cute. Not me. I know I'm not that cute anymore.
[continues sobbing]
Mirai: Oh come on, that's not true. You're very cute!
Kun: [walking away]
Mirai: You're the cutest! Adorable!
Kun: [crying harder; runs away]
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Kun (High Schooler): [off-screen] That's just awful. Yep, a complete wreck. I'm talking about your attitude. Boy, does it stink.
Kun: [looks inside train station, sees a high schooler sitting inside] Hello?
Kun (High Schooler): You're supposed to go camping, am I right? Catch bugs, watch fireworks, all that stuff. And you guys will be staying at your grandparents' place. It's the summer you've all been looking forward to. Think of all the happy memories you could be making together. But instead you don't wanna go. Why is that?
Kun: Uh... how do you know? Who are you?
Kun (High Schooler): What's more important, the color of your pants or your memories? Well, it's your choice. Just go home and say you're sorry already.
Kun: NO. I do NOT like them.
Kun (High Schooler): What?
Kun: [referring to his pants] AND I WILL NOT WEAR THEM!
Kun (High Schooler): [getting annoyed] No, you do not not like them.
Kun: [as a train appears] No, I don't not not like them!
Kun (High Schooler): No, you do not not not not like them!
Kun: Yes, I do NOT not not not like them!
Kun (High Schooler): NO! You do *not* not not not not not like them!
[train pulls into the station. Doors open]
Kun (High Schooler): Don't get on!
Kun: Uh...?
[looks back in hesitation]
Kun (High Schooler): Stop! Don't get on, 'kay?
[whistle blows. Kun glowers at high schooler and bounds for train]
Kun (High Schooler): No! Wait! Wait!
Kun: [glowers at boy as the train pulls away]
Kun (High Schooler): [gazing after it in disappointment] Little brat.