Wealth
Even if his sister and most other Devils and Demons didn't acknowledge that Saphirate Crystals were actually worth something, the truth was certainly different.
Saphirate Crystals had many unique uses.
They could be turned into natural sources of light, ground into a powder that could be used to create Saphira Water, a fundamental ingredient for a large collection of potions, and unique weapons could be created with different types of alloys that required molten Saphirate.
The manufactured goods that require Saphirate Crystals were not of a high rank or quality, but the Saphirate Crystal was still a Circleless D+ Rank item that could rarely be found in large quantities.