Survival Starts with the Black Ball

It's been 16 years... I finally know where I have traveled through time... But I can't be happy... Because in my vague memory, this is a high-risk world, and it is about to usher in a doomsday catastrophe... Alien creatures hidden everywhere, playing with human black balls at will... As the truth is revealed, scenes emerge. What followed was an earth-shaking change in my worldview over the past 16 years. In order to survive, in order to no longer feel the threat of death, in order to live better, I made a decision... I'll start with the gantz manga, and I'll write that one later, so I'll talk about it later~ This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.