[Sunred]

Here is how I group the "eras".

Showa Era Phase 1
Kamen Rider
Kamen Rider V3
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Stronger

Showa Era Phase 2
Skyrider
Kamen Rider Super-1
Kamen Rider ZX

Showa Era Phase 3 aka Metal Hero Era
Kamen Rider BLACK
Kamen Rider BLACK RX

Proto-Heisei Era
Kamen Rider Shin
Kamen Rider ZO
Kamen Rider J

Heisei Era Phase 1
Kamen Rider Kuuga
Kamen Rider Agito
Kamen Rider Ryuki
Kamen Rider Faiz
Kamen Rider Blade
Kamen Rider Hibiki
Kamen Rider Kabuto
Kamen Rider Den-O
Kamen Rider Kiva
Kamen Rider Decade

Heisei Era Phase 2
Kamen Rider W
Kamen Rider OOO
Kamen Rider Fourze
Kamen Rider Wizard
Kamen Rider Gaim
Kamen Rider Drive
Kamen Rider Ghost
Kamen Rider Ex-Aid