The movie is bound to have its funny moments, given the main character is still an innocent, playful little boy even when faced with the difficulties of adjusting to having a younger sibling.
- When Kun's grandmother comes to look after him, she casually comments on how his play room is pretty messy. She gently offers to clean up while he plays with the dog Yukko. The very instant she closes the door behind him, the grandmother frantically panics to herself about how Kun's parents will arrive home with the baby any minute. Bear in mind, the grandmother has spent a brief sequence cleaning up the house, and the nursery Kun was supposed to clean is messier than before!
- When Kun's parents offer Kun to name his then-nameless baby sister, he comes up with names like "Nozomi" and "Tsubame". The mom is the first to point out they're names of bullet trains, which Kun happens to like.
- Also crosses in heartwarming, as his parents are good-humored about it.
- Kun trying to read a story book to a (formerly) napping baby Mirai. But he starts to go on a random (if highly imaginative) tangent about how the storybook characters go on different trains, all the while he puts his toy trains in her basket and slips train cards between her toes. Towards the end of his story, she's covered in train and has an innocent, curious look on her face like she's invested in what's happening.
- "KNOCK! IT! OFF!"
- Kun trying to yell for attention while his mother coaches her husband on how to feed baby Mirai? Sobering. Yukko watching the commotion with the most unamused look on his face? There's something to be said about how the dog is the only sane one.
- During a tantrum over how he didn't ask to be a big brother, amidst his claims that Mirai is not his sister, Kun tells his mother to her face "And you're not my mom!" To this, the mother exasperatedly wonders, if she's not Kun's mother, what does that make her then? Kun angrily fumes that she's a witch, an ugly, old witch! The offended expression on her face drives just screams "Did my kid really just call me old and ugly?!".
- Kun running around the courtyard and house as a Human/Dog-hybrid after removing Human Yukko's tail and attaching it to his own body, even Baby Mirai is amused.
- Kun playing fetch with Human Yukko, emphasizing the fun and attention Yukko's been longing for since Kun's birth.
- Kun covering baby Mirai's face with whale cookies while she's napping, even though it gets him into trouble with Future Mirai.
- Kun and his mother going through her photos, given some of the comments he makes.
- Kun playing with his mother as a child, even though it gets her into serious trouble in the long run.
- Future Mirai tickling Kun to get him to put the dolls away, Kun enjoys it so much, he keeps asking her to do it again.
- Kun, Future Mirai and Human Yukko trying to put away the dolls that Baby Mirai received on Girls' Day behind Kun's father's back.
- Kun's father starts to wonder what is going on and worries he's lost Baby Mirai since she and her Future self can't appear at the same time. Kun is forced to feign a Potty Emergency to stall him.
- Kun and his future self get caught up in a shouting match about Confusing Multiple Negatives, proving how even as a teen, he still engages in petty nonsense when it happens.
- Kun and Baby Mirai laughing and screaming with each other when she smiles at him.
