Each episode is a stand-alone episode of the related parent series, featuring a plot involving some sort of competition, and having a cameo appearance from a character from one of the other series.
Since these cross-over episodes feature a theme of competition, and the Olympics are mentioned a few times, it is likely that this cross-over event with meant to tie in with the Tokyo Summer Olympic Games. They would have been taken place in August 2020, at the same time of this airing, but were postponed due to the COVID-19 pandemic.