A hole in the earth so deep that nobody has mapped its floor, and a town of treasure hunters grown up around the rim. Akihito Tsukushi has been writing and drawing that hole since October 2012, on Takeshobo's Web Comic Gamma, and the chapters fill fourteen tankobon volumes as of August 2025.

Riko is an orphan raised among the cave raiders who work the Abyss, trained to follow her mother down. Reg is a boy she finds in the pit, part machine, with no memory of where he came from. The two of them start the descent together, Riko chasing the bottom and the mother she believes is waiting at it.

Tsukushi draws all of this with round faces, small frames and soft lines, an art style that looks built for a gentle children's adventure. It is not one. The Abyss is dark fantasy, and the series is blunt about the cost the descent imposes on the people who attempt it. Go in expecting the tone the character designs promise and the gap will hit hard. That gap is deliberate, and it is the thing readers argue about most.

The worldbuilding carries the rest. Layer by layer, Tsukushi invents creatures, relics and a working ecology for the pit, then lays them out in dense annotated spreads that reward slow reading rather than fast page-turning.