Disclaimer: I do not own Kingdom Hearts or anything related to it.
Prelude
Twenty years have passed since Sora defeated Xemnas, bringing an end to Organization XIII. Shortly after the final battle, Sora, along with King Mickey and Riku, founded the Council of Keys, or the C.o.K. The Council's purpose was to purge the worlds of the Heartless that remained. An impossible task for three keyblade wielders, they began to scour the galaxy for others capable of brandishing the power of the keys. Their first recruit was found not far off, but close to home: Kairi. Sora trained her how to use her keyblade and her skills heightened greatly.
Another giant step was taken for Sora around the fifth year. He asked Kairi to marry him. She said yes, and one month later they were married on the sandy shores of Destiny Islands by the light of the sunset.
About nine months later, their first child was born, a son. They decided to name him Axel, since he gave his life to save Sora. Axel grew into a strong young man and inherited the ability to wield the keyblade.
By the time Axel was ready to join the C.o.K., there were around fifteen other members working to destroy the remaining Heartless. Around his tenth day with the C.o.K. Axel was sent to the world Disney Castle to meet with the King. This is where our story picks up. A fifteen year old Axel is traveling in a gummi ship to Disney Castle with his thirty-five year old father, Sora.