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

W is the series after Decade so if you want to watch the Kamen Rider seasons in order then watch W after Decade.

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.

Decade is the series after Kiva so if you want to watch the Kamen rider seasons in order watch Decade after Kiva.

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