[Matrixbeast]

Quote:

Originally Posted by MaskedRiderAsakura

I can't speak for Wataru, but you could argue Kenzaki, in his travels, became more bitter. It happened in the Kamen Rider Blade novel.

Doesn't explain Shinji, the technical pacifist, all of a sudden working with other Riders to kill Decade.

It's what happens when you don't know what you're doing with the past characters. The Ryuki in the Rider War was most likely the original.
But it's that it doesn't really matter. Decade begins and ends on the Rider War that yields no purpose. A giant reverse button is always hit, so everything that happens in Decade or the movies that try to explain Decade don't really matter.
The Riders are out of character because Decade needs them to be so he looks more sympathetic in comparison (Or, for the time when he killed Blade and Ryuki, to look "Cool").