A Musclebound Old Man Wants to Turn Young Again and Destroy the World?

Lin Gen, who isn't human, retired of his own accord at sixty. As the head of the dynasty's assassins, he had planned to enjoy his retirement as intended, but then the emperor started chasing him down to kill him. He wasn't afraid of being attacked. What worried him was accidentally slipping up one day and failing to block a strike. The whole world would be buried with him... After all, he wasn't human. He was a higher-dimensional lifeform. The emperor kept trying to kill him, but before he could finish the job, someone assassinated the emperor. Good news: the emperor was dead. Bad news: there were several emperors, and every one of them wanted to kill Lin Gen... They kept coming at him, again and again! At last, Lin Gen slipped up and failed to block a strike. The world nearly ceased to exist! When Lin Gen woke up, he stared silently at the mutated world all around him. Damn it, how was he supposed to deal with this? This was going to be a tough one!