UQ Holder Vol. 15 (manga)

After travelling all the way to Kyoto, Tōta and Kirië finally track down Nagi’s old workshop, where they meet Albert Chamomile, Negi Springfield’s old partner. There, Albert shows Tōta memories from Negi’s past, including an alternate timeline of how Negi’s life would have been if Tōta didn’t exist. Tōta watches from the sidelines as a decisive battle unfolds between Negi and Nagi, and finally sees firsthand the overwhelming power of the two mages that came before him.