A dystopian society emerged. The surface has been scarred and laid barren.  Who knows how long it has been since...  They do not think abt time like that anymore.
Life must go underground.
A father and son  found an abandoned  underground cavern system that has become teeming with life of all sorts , kinds of new creatures that  have adapted and  are thriving. 

They build robots of scrap, programmed for help and company a father and sons image.
The stray cat has become their pet. Completely normal, unbothered, unchanged, and unaffected by the event. It eats the fish caught by the humans and robots.
A taste of normalcy.
The joys of company, companionship, and fishing still endure. life finds a way.
They are the "last bastion"