Thirteen is too young to gain eight years of memories that might come to pass--especially when you don't even know what to do with yourself in the present. But when the future is that bloody and dark, do you have any choice but to try to change it? He remembers the absolute agony of the doctors trying to save him, which finally sent him into blissful unconsciousness— —except he doesn’t remember any of that. Tsuna’s last memory is of putting his head down on his desk and falling asleep to the sound of the teacher’s droning, thirteen years old and tired of not understanding a word, not of being twenty-two and beloved and dying.

Unwillingly forced to serve as a human trial for a crazy alchemist experimenting with time travel, Edward Elric finds himself standing across from Truth in the moment it takes his leg from him. Armed with the knowledge of what's to come and burdened with guilt for the choices he'd made as an adult, Ed sets out to fix every mistake he ever made and save every life they ever lost, no matter what it takes.

or, Catharsis: The Fic In which Wei Wuxian, shortly after being called into Mo Xuanyu’s body, is further forced into the past, where he proceeds to tumble his way into absolutely nailing a time travel fix-it.

After their end, a plea and a wish for things to have been different by Lan Xichen sends Nie Mingjue and Jin GuangYao back in time and gives them a chance to do better. With their knowledge of the 'future' they came from, they have to figure out how to deal with each other.

Nie Mingjue would be the very first to admit that devious plotting was not his strong suit – but if it meant he could make things better, make it so that his brother never had to dirty his hands to avenge him, he would do his best. His best, in this instance, was a forbidden ritual that sent him back in time to before their father had died, before Wen Ruohan's perfidy was revealed, before Meng Yao was twisted by the world's cruelty, before Wei Wuxian was orphaned... Nie Mingjue had a lot to do and very little time in which to do it. Best to get started right away.

Where Class 1-A finds itself in a time loop centered around their first year at UA. After getting over the usual angst, they decide that the best way to grow as heroes is by antagonizing dangerous villains for fun and amusement.