Picked Up by Superman at the Start: A Viltrumite

My name is Shane, an outstanding graduate of Viltrum, and also a traitor to Viltrum. This civilization is too cruel, so cruel that I can't help but miss the peaceful days of my previous life on Earth. For this reason, on the day of my coming-of-age ceremony, I made a major decision. Taking advantage of the moment when the other Viltrum reserve warriors were lax after conquering a planet, I stole a spaceship from that dilapidated unlucky planet, planning to head to Earth for some leisurely time. Even if Viltrum settles accounts with me afterwards. But when I finally arrived near Earth after much hardship, a guy completely beyond my expectations appeared. Why does this Earth have Superman?!