Energy is the bonus story of the second volume of Battle Royale.
Plot[]
This story is a flashback from the point of Noriko Nakagawa, telling the first time she saw Shuya Nanahara and how they became friends.
When she first saw Shuya, Noriko was made to attend a baseball game to cheer on Shiroiwa's team. Shuya caught the winning catch; later that day, he got into a fight with the coach as the coach wanted to cut the boy Shuya caught the ball for as he hadn't won the game, resulting in Shuya being kicked off as well. Shuya tried to cheer up the boy, but the boy told him to stop fighting against the system and making trouble for others.
When they became friends, Noriko visited the orphanage Shuya lived at, only to find him in a depressed funk over not being able to play baseball, which was his passion. One day, Shuya heard a rock and roll song on the radio. Inspired by the energetic music, Shuya gained a new passion and desired to become a rock and roll musician, despite that music genere being made illegal in the Eastern Republic of Asia. Yoshitoki Kuninobu, Shinji Mimura, and Noriko all offer their support, cementing the person Shuya is in the main story.