In a world where gemstones can be used to power magic, it is not uncommon for gem miners to spend their entire lives underground. One day, the gem craftsman Akeboshi visits a village after hearing rumors of a rare gemstone there. It's there that he encounters Kai, a young boy with no family who is suspicious of him because of his red earring. After Akeboshi explains that the earring is standard attire for all craftsmen associated with the Mining Federation, the organization that governs the use of gemstone magic, the two are able to become friends. But when Akeboshi explains that he came in search of a red diamond, Kai becomes furious again.
This is because Kai himself is the red diamond. Some time before Akeboshi arrived in his village, another man wearing the attire of a gemstone craftsman fully petrified Kai's family, and would have done the same for him were it not for the arrival of some of the village's guards. Kai's family now produce jewels, Kai has a red diamond growing in his leg, the only part of his body that was fully petrified, and he and his family have been used as a source of money by a greedy jewel merchant.
Akeboshi is able to defeat the merchant and rescue Kai, and uses his gem magic to create a barrier around his family. Akeboshi then agrees to take Kai on as his apprentice so they can journey to find the man who petrified his family and discover the way to awaken them.
This work contains examples of:
- Action Girl: Kai and Akeboshi are eventually joined by Kou, a talented young woman who is able to use semi-precious jewels in her familiar magic.
- Body to Jewel: The victims of petrification will eventually grow jewels on the stone parts of their bodies.
- Ambiguously Brown: Benito and his apprentice have dark skin.
- Child Prodigy: Kai isn't just a natural as a crafstman, but he also shows more potential than any other partial petrification victim to use the power of his gemstone body.
- Fantastic Racism: The stone eaters are looked down upon in the north.
- The people of the north look down upon people who lack affinity for the use of rarer gemstones, which tend to have more raw power.
- Horned Humanoid: The stone eaters can grow their horns larger by consuming stones.
- Living MacGuffin: Kai is often a target due to the valuable stone growing in his body.
- Phlebotinum Rebel: Kurotobi, the man who petrified Kai's family was a victim of inhumane experimentation by the mining federation.
- Supreme Chef: Kai picked up a lot when working in a kitchen.
- There Is Another: It's eventually revealed that Kai isn't the only Diamond in the Rough. The mining federation views him as a spare.
