So, Mordred shall be our girl. But now I kinda remembered that there are kind two versions of Shirou. So now you get to vote. And before you asked, no, I am not doing Ishtar as the mother, since that isn't Rin, but there is a Sudo-Servant Rin and that basically works.
So, Vote
Muramasa Shirou
Archer Shirou
(NEW UPDATE)
I am ending this poll now. I have thought about it and think I will do Archer Shirou, since Muramasa Shirou isn't actually Shirou. And if I won't do Ishtar Rin, then well, you see where I am going with this. I apologise, but maybe in the future I will do something with a Muramasa Shirou, cause I admit, it's a cool idea right?