I think he turns back in time every time the mc dies. It could or not be time travel and might be parallel universes shit because some things are different than how he remembers i think he stated that but he comes back to save the mc 'this time' every time.
But considering the mc doesn't have any memories of the moment apocalypse begun and fainted/woke up in the middle of it makes me think he might have time travelled or whatever happened to ml as well but just doesn't remember.
is the ml a time traveler? that could only explain everything right? or why does he remember a past the mc doesn’t know of,,,