We all know the story: a mermaid ventures to the surface, falls in love with a human man, and ultimately ends up dying because of it. A Sinner of the Deep Sea takes Andersen's tale and reframes it, asking what would have changed if the mermaid had a best friend who wouldn't just sit back and let her die, turning the narrative into something recognizable but still very different from the story we usually hear.

In this case, the mermaid is Ryuu, a famous mermaid dancer and fairly major celebrity. Her best friend is Jo, a much more prosaic woman who just seems to enjoy living her life as she pleases – playing with whales, sunbathing on the surface (far from shore, of course), going out to eat…just the basics, thank you very much. But her life is upended when Ryuu doesn't show up when they plan to meet. She discovers that she's broken the greatest of all merfolk laws: she's gone to the surface and interacted with a human. Ryuu's unceremoniously clapped in jail by Akira, a border patrol agent, and it's up to Jo to unwillingly figure out what to do for her friend from there. It's a fairly basic twist on the typical story, but Tomi manages to make it feel engaging and special with the characters and world-building, both of which are outstanding.

The latter is probably the highlight of the book. In Jo's world, merfolk have established their society in the abyssal depths of the sea after interactions with humans centuries ago went poorly. Now merfolk society is hidden by giant reefs and other seabed structures, and the people have developed bioluminescence to cope with it. Their society largely functions the way humans do, and Tomi takes care to even show the little details; for example, to be fully dressed, we see that a merperson must have their nipples covered (gender notwithstanding) as well as the area of their body where the fins meet the flesh of the torso. It's never explicitly stated, but scenes of Jo and Ryuu getting undressed for bed make it clear (as do crowd scenes), which also implies that wearing more clothes indicates a higher social class: Jo wears the bare minimum and is turned away from a fancy restaurant, while Ryuu shows up in a long coat and is instantly welcomed. Other good details include the little weights on blankets, the use of empty quahog shells for wallets, and porthole-cover style doors, all of which show that Tomi was really thinking about how life under the water would function.

The art is also a major draw. Tomi's art looks like fanservice rounds out the artistic offerings, feeling largely natural in the story's settings. Most interesting is in volume two, when Yuki, the human Ryuu's in love with, meets Jo, who has accidentally gained legs by consuming a special pill. Jo doesn't think anything of her barely-clothed state (although when she and Yuki return to the water later, we see her rapidly putting her top back on after taking it off briefly), but Yuki has a hard time not looking at her torso and legs. This shows the difference between how merfolk and humans view their bodies, and it's remarkably effective.

The first volume doesn't have much going on in the way of plot beyond setting things up. Jo's grudging determination is the main takeaway, especially when contrasted with Ryuu's almost ditzy demeanor: Jo is just living her life while Ryuu is always searching for something newer and better, with the implication being that her attraction to gangly marine biologist Yuki may have more to do with him being new than anything deeper. (And that might go for him, as well.) Volume two ups the ante significantly with Jo taking on a different aspect of Andersen's Little Mermaid's role as she turns human and goes to find Yuki. This puts her in direct confrontation with law enforcement, including Maya, who has had creepy feelings for Jo since she was thirteen (and he was an adult), but more importantly, it really lays out the differing factions within mer society. Jo, Maya, Akira, and Ryuu all represent something different, and how things will get sorted out is tensely unclear.

Volume three, which completes the series, brings everything full circle as it explores the political ramifications of Ryuu's and Jo's actions. There's more going on than Ryuu simply falling in love with a human, and those feelings are revealed to be closer to fascination than love, fascination that someone in power was able to take advantage of. Like Andersen's young mermaid, Ryuu is naive, and it is Jo and Yuki who have to take control of the story in order to bring it to a satisfactory conclusion. It's not an ending that will please everyone, but it's one that makes sense and continues to play with Andersen's established tale and mermaid lore.

A Sinner of the Deep Sea is a nearly-perfect three-volume series. I wish it could have been longer, because this is a world and characters who are so well realized that it feels like a shame to bid them farewell so soon. But ultimately I think it might work because of its brevity. It makes its point and leaves the aftermath open to our own imaginations. The story goes on - we just have to think about what that means ourselves.