Kamen Rider Decade (2009)

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 are heisei anniversary seasons celebrating their respective decades

both use returning actors

Both are seasons of a Toei tokusatsu franchise: Zenkaiger for Super Sentai and Decade for Kamen Rider. They have a heavy focus on being the anniversary of the franchise. Both seasons have a focus on the franchise being part of the bigger multiverse. These multiverse worlds correspond with a previous season of their franchise. They also have a gimmick that has the power of those seasons stored in them.

Both are shows about transforming into past heroes
Both appeared in Kamen Rider × Super Sentai: Super Hero Taisen