(But more seriously, it's for type moon's april fools joke where Satsuki, Sion, and Ries go on an adventure to overthrow the various main heroines, and Ciel and Saber join them, Ciel either because she's bored or she wants to smack Arc, and Saber disguised as 'Mysterious Heroine X' with the objective of beating down all the Saber clones)
Tangerang said: It is mysterious heroine X. Whoever could it be?
(But more seriously, it's for type moon's april fools joke where Satsuki, Sion, and Ries go on an adventure to overthrow the various main heroines, and Ciel and Saber join them, Ciel either because she's bored or she wants to smack Arc, and Saber disguised as 'Mysterious Heroine X' with the objective of beating down all the Saber clones)
I can understand why Ciel wants to join: She's often consider the scrappy heroine of Tsukihime. I'm surprised Sakura didn't join up, though I'd imagine she'd recognize Saber
