Piccolo Day is held on May 9. This is the day that King Piccolo declares his ruling of Earth in "Tenshinhan's Resolve" and "Prelude To Vengeance". In the Funimation dub, this date was localized to the 13th to keep the association with bad luck (9 being an unlucky number in Japanese culture).
King Piccolo says that he will take a slip from the box (being held by his son, Piano) each year on the Piccolo Day, and the chosen sector on the slip will host that year's celebration and will end in its destruction at the hands of King Piccolo himself.
The ceremony is celebrated by King Piccolo once, in Age 753. The only sector chosen among the 43 sectors on Earth is sector 28, the location of West City. However, the city is not destroyed due to Goku killing King Piccolo on this day before the latter left Central City.
- This is also the day that Drum and Piccolo were born.
- Goku gets his new Flying Nimbus from Master Korin and kills King Piccolo on this day. This day also marks the end of the King Piccolo wars.
- The real-world Japan Anniversary Association recognized on May 9 as Goku Day. This is because the numbers 5 and 9 can be read in Japanese as "go" and "ku", respectively.
- This date however is quite fitting as it was the day Goku defeated King Piccolo, which was one of his only heroic acts to be recognized by the government and the general public of Earth (at least when it was still fresh in the people's minds as it was largely forgotten by the time of the Cell Games).
- May 9 'Officially' Recognized as Goku Day. Anime News Network (May 9, 2015).