Comet Lucifer

Comet Lucifer (コメット・ルシファー, Kometto Rushifā) is a 12-episode Japanese anime television series produced by 8-Bit and directed by Yasuhito Kikuchi. It aired between October 4 and December 20, 2015. The anime has been licensed in North America by Sentai Filmworks.

Plot
"Gift" is a world where glittering blue crystals known as Giftium are buried deep underground. A young boy named Sōgo Amagi lives in the prosperous mining town of Garden Indigo, whose hobby is collecting rare crystals, one day becomes involved in a dispute between classmates Kaon, Roman, and Otto. He wanders deep into the ruins of a mine and discovers an underground lake. There, Sōgo meets a mysterious blue-haired girl with red eyes named Felia and their fateful meeting is the start of a new adventure with their newly formed bond.