Kai is a strong and determined boy. It is loyal to friends, and does everything for them. Kai is one of the strongest disciples of Master Funen, and the Great Child of Trios, the Third World. Kai meets Pinky and Bucky when they are going through Trios, and decides to accompany them on the journey to Spaak and the World Zero. Since childhood he is grateful to Spaak, who saved his village Monster Troublemaker Taurus Giant (the same village Spaak saved again with the help of Bucky). Since then much Kai trains under the tutelage of Master Funen, which was also the victim of a curse cast by the "Needle Tower". The reason to follow up with Bucky in Zero World is training to become stronger, and find Spaak in order to thank him.