Card Descent: I Can Fuse and Upgrade Cards

Three hundred years ago, glowing portals began appearing across Blue Star. Beyond each portal lay another dimension. A portal remained open for one month. If the demon beasts inside were not dealt with in that time, it would shatter, releasing them into the world. Modern technology was powerless against these beasts. Just as humanity was giving in to despair, cards descended. When they reach adulthood, everyone receives ten cards to form a deck. Anyone with at least half of their deck made up of cards ranked C or higher can become a Spirit Card Master.