>erasing Death is a plot point
>whole arc about how humans eventually turn into trees if they live for too long
>most important character is a Chainsaw
Denji and Asa will grow old together and fuse into a tree (like the one in Fire Punch). Centuries after society collapses, Pochita shows up to chop them down. Nothing was resolved, and Denji can't be a hero no mo'. There, I solved your manga.