Rider Time: Kamen Rider Zi-O VS Decade (2021)

Both focus on high school students trapped in their school and forced to fight.

However, Girl Gun Lady has the characters going into an alternate reality in-show, while Kamen Rider Zi-O VS Decade is just full-blown set in a reality that is not the one from the main TV show.

I recommend this both drama because , Male lead and Female lead
try to solve problem
In one drama explosion and another student murder/suicide

Both feature Kamen Riders from multiple series
Both have a murder mystery to be solved
Both are spinoffs from a main series