In the story of "Battle Royale of Balls", you become a challenger in a spaceship. Since the spaceship entered the wormhole by mistake, and faced the grave danger of disintegration, you have to choose battle to begin your doomsday escape.
During the challenge, the danger zone in galaxy will expand gradually. At the same time, the safe zone will shrink and it eventually will disappear completely. In the battleground, your ultimate goal is to become the last one standing.
In the process of the challenge, eating meteorite thorns or other challengers can accumulate the shield. Only after building up the strong shield can you protect yourself in the danger zone.
Without the shield, your weight will dramatically reduce until death when you are exposed in the danger zone. Just like living in a deserted island on Doomsday, only killing others can help you survive.