Anime: Comet Lucifer
Gift, a world covered in glittering blue crystals called gifdium. Sougo Amagi is a boy who lives in the town of Garden Indigo, which has prospered from the mining of these crystals. Sougo, 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, Sougo meets a mysterious girl with blue hair and red eyes. Who is this girl, and what will their meeting bring? The door to an adventure opens with their newly formed bond.