Astronauts: Sirius - Verethragna ~Seisen no Duelist~

The trading card game Verethragna is a game created by the world’s largest game company Link World. Players summon and fight with gods and demons, heroes and monsters summoned from other worlds. It has become extremely popular, with people of all ages addicted to it.
Tatsumi, the head of a zaibatsu, was trapped by the Kokuryou Gakuen’s chairwoman Metsheila into a hidden duel tournament. He suffered a horrible defeat and was bounded from leaving. She sent a challenge to his son, Akira, telling him to fight to the top of the duelist ladder at the school if he wished to exact revenge for his father. Accepting her challenge, he enrolled as a student at the school.

One day, when he accidentally wandered into the woods behind the school, he encountered unidentifiable monsters. However, he was saved by a card of Kiskill, the dark armor-wearing goddess of darkness. He fought up the ranks with her by his side, was selected as one of the 21 knights (ritter) and aimed to become the ‘duel kaizer’. What is the Metsheila’s intention and what is the truth behind Verethragna and the other worlds?