Griffinhart said: Half-sister, IIRC. Toosaka Tokiomi had an affair in London, and Extra!Rin is the result. FSN!Rin is actually Extra!Rin's mentor.t
She's quite a bit younger than FSN! Rin though from what I remember. I remember on the Extra website, or perhaps the CCC one, that it shows a scene where Extra! Rin is playing in a kiddie pool as a child and we see FSN! Rin, eclipsed by the sun, and she's like an adult or teenager or something.