Let's use the website of "JNTO" for tourism in Japan!

Article　https://osusumeseikatsu.com/en/japantourism/
This homepage is largely divided into "By Destination" and "By Experience".
In the "By Destination" section, you can search for sightseeing contents by keywords of cities and regions you want to visit in your trip to Japan.
In the "By Experience" section, you can search for sightseeing contents by season or category.
You will be able to find events that you can only experience during that season, in addition to the events you were aiming for.