THE HUNDRED-YEAR CRYSTAL CATALOGUE

Bentt, a traveling scholar, comes across a young man named Iris in an abandoned mine. Iris eats crystals, has eyes that sparkle like rainbows, and is the last surviving member of a race known as the Diamonds of the Desert. Setting out on a journey together, the two begin to slowly open up their hearts to each other. However... (Source: Printemps Publishing) Note: Includes one extra chapter. — Description from AniList community (anilist.co).