[Kamen Rider Die]

I mean, obviously the answer is Accel (dude says Henshin like he's passing a Gaia Memory), but just to have some other opinions, lemme stump for the laid-back dark reflection of Ryuki, Ryuga. I really like the way he doesn't shout "HENSHIN!", he just says "Henshin." It's somehow more terrifying when someone treats the Henshin less as a primal will-to-power, and more as a Well You Just Missed Your Last Chance To Avoid Me Killing You, by-the-by sort of thing.