Quote Originally Posted by Kitten Champion View Post
Oh~ Okay. You need to do the Story Gacha specifically and can't get him from any old rate-up banner. I just assumed he was in the general pool after Orleans.

I guess Cu Caster was on a banner where he was also included and I didn't notice, along with Artoria Lancer Alter who I believe is also story locked.
You do get a Caster Cu as part of finishing Fuyuki.