Earth's Doomsday, I Have a Northeast Cellar System

In his past life, a devoted classmate gave her life to protect him when the apocalypse struck. Reborn before the doom, he is granted a high-tech bunker system. Determined to change their fate, he finds her and builds an impenetrable underground sanctuary. Safe from the chaos and radiation outside, love blossoms as they raise a family in peace. But as the toxic smog on the surface finally clears, will stepping out into the ruined world bring a fresh start, or deadly new threats?