Tsuna and Gokudera are trying to revive Shoichi Irie. They succeed, but Shoichi tries to get them to continue the game and says that he would gladly die if it meant the defeat of Byakuran, confusing Tsuna. Tsuna states that he couldn't see the point of defeating Byakuran, and that he only wanted to return to the past, and Gokudera agrees with him. Shoichi grows agitated and insists that defeating Byakuran is important. Tsuna is confused and presses him for an explanation. Shoichi then explains the reason why he wants to defeat Byakuran.
Eleven years ago, he once helped Lambo when Lambo flew into his apartment and, as a result, received a wooden box from the Bovino Famiglia as a token of gratitude, as well as some Ten Year Bazooka shells for Lambo. Shoichi forgot to give the shells to Lambo and one day, he accidentally dropped one on himself, causing him to travel to the future. He ended up in an engineering university and started to panic. That was the place where he met Byakuran, who commented on his young age in university just before Shoichi returned to the past. Shoichi continues to explain that he tried to change the past in order to change the future and be a musician and also tries to start explaining about parallel worlds when the Vongola members arrive to treat his wounds.
As Ryohei heals Shoichi, Reborn explains the theory of parallel worlds where the past branches off to different futures and that different future co-exist. Shoichi then reveals that he burned his textbooks and used the ten year bazooka on himself again after seeing the future. He ended up in a future where he was a musician in a rundown bar, in a foreign country. He was being chased by some sort of gang, but ended up meeting with Byakuran again. That Byakuran knew about the other world's meeting through slow memory transmission (albeit painfully, as it was his first time, the process also being the way Byakuran transferred memories to other world counterparts), which caused Shoichi to run away in fright, and the latter returned to the past shortly after that. Frightened of what he saw, Shoichi decided to work hard again and get into a university. About a year after he last used the bazooka, he tried to use it again and ended up in a world where all the buildings were reduced to rubble and Byakuran was the dictator of the world. He used the bazooka shells many times after that, but every time he used it, he ended up in a world ruled by Byakuran.
Shoichi continues to explain that parallel worlds were completely different from one another and that the ones in a particular world should not be able to contact the one on the other, but Byakuran has the power to share all his knowledge and thoughts from his other selves across the multitude of parallel worlds due to possessing the Mare Ring.
*Note: Bold + Italicized = First Appearance