Rin knew the Servant got along with her well enough but didn't know if she would accept such a request. Nonetheless she had to ask here and so ask she did. There was only one condition.
"After I help you with this ritual you have to be my servant for a week. That includes any requests to dress up like a maid or nurse or sweet, sweet Ayako-chan~" All things considered Medusa could have made much worse demands. If a week of servitude was what it took then Rin felt that it was worth it. She then led them to her bedroom after making sure that Shirou and her sister had left.
Soon enough Rin started to give Artoria gentle kisses before increasing their intensity. Meanwhile Rider began grinding up against Rins backside while nibbling at her earlobes. Rin started to unbutton Saber's blouse, pausing a bit for Rider to remove both her own turtleneck and Rin's. Saber was without a bra, Rin supposed she really didn't need them given her small breasts. Rin marveled at Rider generous bust, sweet ass, and, long beautiful legs. She also marveled at Saber who was beautiful in a more regal sense. Soon enough they were on the floor with Rider on top of Rin and Saber to the side, all of them bereft of clothing with the exception of Rin's thigh high stockings and Rider's glasses. Rider positioned her clit in front of Rin's mouth while she stuck the magus' now hard cock between her generous bosom. Rin began lapping at the woman's folds and savored the taste as Rider started pumping the cock between her tits. Rin wrapped her stocking clad legs around Rider's head as the Servant licked at the tip of cock as she picked up the pace of her pumping. Saber meanwhile began to touch herself as she got on the floor and began licking at Rin's anus. Rin shuddered at the pleasure from the new sensations she was feeling, both from her new appendage and from her previously untouched hole. Rider's tits were hot and beginning to get sweaty while Saber's tongue felt odd but pleasurable in her virgin anus. Soon enough Rin cock spurted a generous load onto Rider's face as the lilac locked lady came herself from Rin's ministrations. Rin and Saber then licked the cum off of Rider's face and glasses and savored the taste.