IIRC Aoko used the Fifth Magic to draw energy from past and future/timelines/whateverthefuckit'scalled to go Super Saiyan and revert Soujuurou. Simply put, she got a magic remote that can fast-forward herself to a time where she's in her peak performance and reversed Soujuurou back. Which is contradicting her lines in MB about the Fifth being just a time travel magic plus the permanent red hair issue, but I could be missing some explanation.[spoil]
[spoil]she activated the fifth magic only because she wanted to revive soujyuurou. there was an implied reluctance on aoko's part to use the fifth magic (the exact reason i am not sure). she took 10 years from soujyuurou and added to herself in order to be able to contend with touko. then there was some implied time-energy equivalence-shit about soujyuurou's 5 minutes. aoko said she left it in the future, and when the time comes she would throw it back to the past, much to touko's rage. then there was shit about the screwup in energy balance leading to the universe's 熱的æ». so wtf?