There have been many stories – even just told with animation – about love going beyond cultural lines, appearance, even specifically love between man and mermaid. As the film settles in to its premise, ChaO has a lot of work to set itself apart from these other films. Director Yasuhiro Aoki builds those necessary idiosyncrasies almost entirely through a goofy sense of humor, even as the Little Mermaid-adjacent story beats persist.

The story, set in an undisclosed near-future (“20XX” is the year we get) in Shanghai, society has evolved to accommodate humans and mer-people living side by side. Tunnels of water soar through the air like highways, citizens of the city come in an incredibly wide range of shapes and sizes, and variable number of tentacles and fins. It starts from the perspective of a junior reporter, late for an interview as he takes one of these highways. One stressful journey later, he begins to talk to Stephan, who tells him his story – of a romance which united humanity and mer-people amidst socio-political tension.

The romance in question is with a mermaid princess: Ao Soni ChaO Neptunus, who Stephan nicknames 'ChaO.' She arrives in his life by accident (or providence?), saving him from disaster at a dock in the city. ChaO quickly proposes marriage, and Stephan tentatively agrees to date her and see. It's built on shaky foundations – Stephan was once an engineer developing 'AirJet,' an alternative to blade propellers which he hopes will protect merpeople and other sea denizens. The idea is shot down for a lack of profitability, but ChaO's family connection means that his boss would reconsider.

There's also the matter of ChaO quite literally being a human-sized fish, an appearance which apparently is conditional of her appearing on land, and not being entirely comfortable there (her appearance changes to a slender and humanoid form when either underwater or made to feel at home). The jokes around ChaO changing form feel a little torn from bottom-of-the-barrel studio comedies from decades past, as do a small handful of gags early on in the film.

Thankfully, these are pretty few and far between; ChaO is very sweet and sometimes even surprising, particularly when it gives itself an incredibly long setup for a joke to pay off later. Over the course of the film the relationship pushes a little more beyond being a symbol of peace for some and profit for others. It's not exactly ground-breaking, but it's pleasant enough. While ChaO's story is familiar, it's significantly buoyed by its visuals. That's not just in terms of it being a pretty palette to look at, but also in accentuating the jokes. The film's best jokes are often a silly and imaginative still drawing, a goofy background character or an piece of incidental world design. What's more remarkable is art direction, courtesy of Hiroshi Takiguchi. There's such immense visual density in its world design, teeming with life in the way a coral reef would, rendered with charmingly scratchy linework. And amidst the cartoonish chaos of the city, ChaO's visual design is also dense with jokes, packed into that same gorgeous and unique imagery.

The animation under chief animation director Hirokazu Kojiima (also character designer - special shout-out here for how everyone's facial features have hidden fish shapes) accentuates the relentless pacing and ludicrousness of the film's comedy. It's always good for a laugh, whether it's in outsized expressions like Stephan's eyes and mouth levitating off his face in a moment of shock, or smaller touches like how ChaO walks around on her tail fin in big sneakers. It's these little things which add up to ChaO being a good time – despite some visual jokes which feel like they should have been left in the past, those are not enough to sink the feature entirely, especially when a lot of it's other gags pay off in unexpected and delightful ways.