Episode 5: The Strongest Builder

Before the decisive battle with Tatsuya Yuki, Reiji once again goes in search of combat practice, while Sei concentrates on fine-tuning the Build Strike. China is becoming concerned that Sei is too engrossed in his work. Then, a mysterious boy named Mao Yasaka appears before the two of them. Having won the Japanese 5th Block, he has already earned a place in the World Tournament, and he says he has come to the store because he is interested in Sei, a highly skilled builder who is the same age as he is. Mao has only one goal: to determine which of them is superior as a Gunpla builder. Sei accepts his challenge, and Sei and Mao bring out their Gunpla, the Build Strike and the Gundam X Maoh. As soon as they see each other's work, Sei and Mao find themselves adrift in space...!