Okay so this worldbuilding is actually really clever and I didn't expect that from what I thought would be a fluffy rom-com setup. You've got this kid who's basically a tiny alien scientist crash-landing on Earth, and the way the author reveals the world through her reactions is so much better than just info-dumping.
The seafood scene hit me the hardest. When she eats that tuna rice ball and her eyes light up like little stars—"So this is what seafood tastes like!"—and then we get the backstory about how oceans got polluted and fish became infected with a virus fatal to humans... that's when it clicked. These people migrated to planet Cang'ai, had a century-long war, and now seafood is basically a historical artifact. She's only ever seen it in documentaries. The fact that a simple convenience store rice ball makes her feel like she's savoring the finest delicacies from land and sea? That's worldbuilding through emotion, not exposition. Brilliant.
And the spaceship stuff—"The Little Fish is a spaceship I built with my own two hands"—this kid is three and a half and already building spacecraft. The self-cleaning spacesuit, the watch-like docking device that makes the ship appear overhead. The author never stops to explain the tech; it's just there, treated as normal by the character, which makes it feel even more real.
The film set scenes also ground this in a very specific Earth reality. Yan Xingli is a celebrity, there's a magazine photoshoot, a show called "My Little Kid" being planned. It creates this funny contrast between the mundane entertainment industry world and the sci-fi elements. The RV on set, the claw machine arcade, the children's clothing store—all of it feels lived-in and specific.
The guest room scene where she gets her head stuck in the clothes is such a vivid, almost cartoonish image but it works because it's grounded in physical comedy. "His round head wrapped in clothes, his two little hands frantically tugging at the fabric, huffing and puffing as if pulling up a carrot." I literally laughed out loud at that.
What I love most is how the world feels like it has history behind it without the author forcing us to absorb it all at once. The pollution, the war, the migration—it's all woven into Qi Youyu's personal experience of being on Earth. Every time she encounters something ordinary (seafood, cartoons, zodiac signs), we get a piece of the larger world through her confusion or wonder. That's how you do speculative fiction, honestly. Let the character's naivety be the lens.