Yuki Judai's diary:

On August 9, 2012, I traveled to a strange world. The people here were very good at dueling and had a lot of summoning methods that I had never seen before. I couldn't beat any of them, but fortunately I returned to my own world safely in the end.

On August 12, 2012, great, the written test results are out. Because of that time travel, I was able to write a question that I didn't know how to do before, and I got a good score of 79th in the written test! But why do I miss the duelists in that world?

On August 25, 2012, I traveled to that world again. Damn, why can't I beat them!

......

On March 3, 2013, the principal said that there is a terrorist organization called Seven Stars in our world?

On April 9, 2013, the Seven Stars have been solved. They are so bad.

.......

Hey, is it the gate to the new world! ?