Kai was a big brother searching for his lost sister, who disappeared during the Time Zone War. The Fast Zone, tired of peace after a whole 1,000 years, had a bored king who launched an attack so swift that no one had time to react. In the chaos, Kai's sister vanished, his mother died, and his father lost his life in the war. Kai was born with a unique ability called "Zone 0," which created a protective area around him where anything approaching would slow to a complete stop. However, without guidance, he struggled to master this ability. People often resented Kai, leaving him with no one to rely on, so he learned what he could on his own.

Fortunately, Kai had a cat named Danger, who was like family to him. Danger was his best friend and the main reason he chose to do good rather than resort to mischief. One day, he watched Danger face off against a snake, amazed by the cat's lightning-fast reflexes, which had a reaction time of around 20-70 milliseconds. Kai noticed that when he mimicked Danger's defensive moves, Zone 0 responded more effectively.

The next day, an old man came to Kai's house and said, "Your parents wanted me to tell you something when you turned eighteen, but I'm old and may not live long enough to tell you." When Kai asked what it was, the man revealed, "You have a sister." In shock, Kai listened as the man explained that she had been taken to another zone, though he didn't know which one. Memories flooded back to Kai—seeing a broken bridge and his mother and sister on the other side, his little sister crying out to him.

Determined, Kai began to pack his things. The man asked, "What are you doing?" to which Kai replied, "I'm going to the Frozen Zone." The man handed him a mysterious sphere, saying, "Take this before you leave. It will allow you to enter any zone. It contains money and a special orb you can only eat if you're in grave danger." Confused, Kai asked, "What does it do?" The man explained, "It will clear your mind and strengthen your Zone 0, but don't eat it unless absolutely necessary."

Kai thanked the man, hugged him, grabbed his pack, and with Danger by his side, they ran toward the sunset. "Come on, Danger!" he called, knowing the cat was known for bringing trouble home, like snakes and other risky surprises.