About Touhou's Ibaraki Douji's Arm and Ibaraki Douji

Since Ibaraki Douji's Arm and Ibaraki Douji are respectively Kasen's "evil counterpart" and true form, should they be implied to Ibaraki Kasen, or kept separate?

As far as I know, they're separate characters, not alternate forms of the same character. Ibaraki Douji may be a fusion, but the Arm is definitely her own character.