Cloud has an accident with a Time materia. If he wants to save the world, there's a person who has to die.

Originally, Gaara thought the plan - brought to him by a desperate and shaken Naruto on the last holding place of the world's few remaining shinobi - was both insane and impossible. No one ever accused Gaara of being sane, nor sensible, so he agreed anyway. He hadn't really expected it to work.

Hibari Kyouya travels in time and takes over the world. Basically crack.

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.