Katekyo Hitman Reborn!

As Irie recovers from his injuries, he explains to Tsuna and the others about why is he obsessed with Byakuran. Using Ten-Year-Bazooka ammo he had received from Lambo's family 11 years ago, Irie went to the future and ran into Byakuran. When he revisited it, hoping to change, it awakened Byakuran's ability to retain the knowledge of different parallel worlds. Byakuran used this knowledge to conquer and destroy several parallel worlds. Eventually, the future Irie arranged for the younger Irie's memories to be temporarily wiped for five years in order to gain Byakuran's trust, since the current world is the only one that is not ruled by Byakuran.