[SengalBoy]

Damn you Die I was meaning to ask this question lol

Let's see how many Riders does this (I don't include the Showa Riders because I don't watch them and it seems like the majority of them receives powers on their debut)

First time transforming:
1) Kuuga
2) Ryuki
3) Faiz
4) Kabuto
5) Den-O
6) Decade*
7) OOO
8) Fourze
9) Gaim
10) Drive
11) Ghost
12) Ex-Aid
13) Zi-O
14) Zero-One

Already a Rider:
1) Agito*
2) Blade
3)Hibiki
4) Kiva
5) W
6) Wizard
7) Build

* Decade is an anomaly since he transforms for the first time in his debut but we know he had been Decade before he has amnesia. The same follows with Agito however I included him in the Already category since it shows flashbacks of Agito in the past while we never see pre-amnesia Decade.

My guess is that I prefer the Already aspect since not only it skips the origin story but also allows the origin to be told as a crucial flashback which worked really well on Captain Marvel.