I think it is a chinese novel although not sure. It's about a guy who survived in a zombie/mutated beasts apocalypse, then he dies and is sent back just before it happens. He has a sister that he teaches how to fight and uses blades but he can't use advanced moves because his body can't take it. The zombies(?) have some crystals that you absorb to get stronger and he later tries successfully to fuse with some mutated ant genes. This is everything I can remember.
There's a manga like that called "King of Apocalypse" but I dont think I was able to find a novel for it when I checked.
It could be but I remember reading a novel. Anyway it's totally the genre I'm looking for so thank you.