Once the Chōjin Tournaments were dominated by a powerful being, the legendary Neptune King. However, he became disgusted as the competition shifted from strong vs. weak death matches into a commercialized sport. He then went into hibernation under in the River Thames. He remained there for millions of years until he was discovered by a Chōjin named Kenkaman. Kenkaman was trying to commit suicide by jumping into the river because he couldn't find any opponents strong enough to defeat him (even Robin Mask was too easy for him). Together, the two of them plotted to bring the Chōjin competitions back to its bloody roots. The Neptune King gave Kenkaman his Neptune Mask, making him Neptuneman, and created a new Bogu-clad identity for himself- Big the Budō.