[Pineapple924]

I think this is the first time I've seen a rider series where they do the "Main rider is turning-into/actually-was a monster the whole time" arc this early in the show, usually its near the end.

-------------------------------------------------------------------------------------------
Speaking of which, I honestly don't know whether to trust Dan's explanation or not.

On one hand, it fully explains how M was first infected, with Emu supporting it when he mentions he started getting serious about becoming a doctor 6 years ago when he passed out after winning the game tournament and "dreamt" that he was being operated on.

On the other hand, this doesn't explain the why Dan had to kill Kiriya but can freely talk about it to Taiga. Especially when he says Kiriya was trying to cure M, but Kiriya's last words didn't imply that at all. If anything, Kiriya's last words actually seem supportive in this context now that we know that the Emu personality is a Bugster:

"Emu... It's up to you to save humanity now..."

"Don't forget... As long as you can smile, you will always be you!"

Either way, there's definitely more to this the story than Dan's letting on, so I'm guessing that Kiriya found the real/whole truth when he went to Dan's father to get some information, and Dan is just trying to keep the other riders busy until Kamen Rider Chronicle is completed.