Kamen Rider W (2009)

Both shows share a dual of protagonists (Shotaro and Philip/Eiji and Ankh) who work together to fight the monsters of their respective series (Gopants/Greeeds). The transformation gimmick of both main Riders uses different kinds of combinations which allow them to activate various forms.

They're Kamen Rider series that has the primary Kamen Rider as a detective and involve them solving case that involves the antagonists. The main characters of each series are very well liked and brings a very cool or should I say hard-boiled feeling to them.

Build comes before the 20th Heisei anniversary

W comes after the 10th Heisei anniversary

both have dual colored riders

both have an ultimate form accessed by rider fusion