What manga is this?

Hi pls help me find this manga. It started with mc waking up from a comatose in the hospital. He was in comatose bcuz he was bullied. When he woke up the world has fallen. It was invaded by robotic aliens?? Turns out one of them were his descendants. They came from the future and they were trying to prevent humanity from extinction i think i forgot my memory kinda hazy. They trained him in an alternate space fighting those robotic aliens.