- It could be a tycoon game about a festival in your country.
- A puzzle/platformer where you need to go to different places to "activate" different artifacts needed to start a celebration
- A cooking game about traditional foods
- A game about Santa Claus delivering presents for Christmas (or some other festivity in another country)
- A game about traditional textiles, similar to this https://store.steampowered.com/app/1075170/Weaving_Tides/
- A rhythm game with traditional music
You can interpret the game as you see fit. You can make it about a tradition of a specific country, time of the year, or even past traditions such as medieval knights' traditions or traditions of different places and times. Even fictional traditions of alien species or something that you create as a narrative. Just take into consideration that you'll need to explain the tradition in some way as adherence to the theme will be one of the factors the game will be judged upon.
Check the theme reveal video for inspiration https://drive.google.com/file/d/1_DK6MD7trOu_BzgL6kFGI6fTpf0ew_9C/view?usp=shari...
Here's the first paragraph of Wikipedia about tradition:
A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or impractical but socially meaningful clothes (like lawyers' wigs or military officers' spurs), but the idea has also been applied to social norms such as greetings. Traditions can persist and evolve for thousands of years—the word tradition itself derives from the Latin tradere literally meaning to transmit, to hand over, to give for safekeeping. While it is commonly assumed that traditions have an ancient history, many traditions have been invented on purpose, whether that be political or cultural, over short periods of time. Various academic disciplines also use the word in a variety of ways. More Info https://en.wikipedia.org/wiki/Tradition
Take the time to brainstorm and think about a compelling idea that adjusts to the theme.