MC is reincarnated and now is the 4th times. But even he tried the best in his past life, all ended with him being killed and the world destroyed while facing armageddon.
In this 4th life. He became realist and apathetic while inside he is still struggling against the world system that toying him all the way during his plan to save the world and avoiding his death future.
To put it simple "world system toying MC, MC toying others to avoid bad circumstances on MC lives and goals, the world system disagree and play it's card againts MC while MC desperately trying to slip off the system.
Up to chapter 65. MC really struggling. While putting his funniest faces, he is wreck inside. He is aiming to change the whole world system, but to change it lots and lots of thing he owned he must sacrificed (include the possibility of his future). If you are asking why he push himself to do it? Well the answer if he didn't do it, he must face repetitive despair in his circle of reincarnation (not to mention repetition of world destruction). It's a vicious cycle.