Hmm, interesting.
I wonder, how would he feel about the idea of a threesome with Rin and Rider? Because Rider will definitely be after Rin too, and she is a rather kinky person....
He'd definitely be up for that. He has no problems with Rider, but he will make it clear to where his claim lies.
Plus he knows that Rin likes girls too, and would have no problem in bringing in a third party for Rin to indulge herself with.
Yeah, Rider would be fine with that, she's not really after a long-term relationship. Particularly with someone who she's ultimately going to have to leave (she wouldn't want to deprive Rin's Sakura of a sister, and she wouldn't be willing to abandon her own master). Plus, if she wanted a long-term relationship with Rin she's got her own version to go after.
And, anyway, she's well aware of Rin's interest in Archer, so she wouldn't
expect to out-compete him. And, I suspect Rin and Dark Archer could dom the
hell out of Rider, which she would enjoy. Or, alternately, she and Archer could dom the hell out of
Rin, which she would enjoy just as much....
I can see her needling Archer and Rin a bit, though, and seeing if they'll "punish" her for it. She tries to get Sakura and Shirou to do so sometimes, but they're mostly interested in each other (they might have the occasional threesome to spice up their sex life a bit) and are also aware of her intentions and, thus, don't use it as a punishment.
Not to mention, he is going to have some fun with MOS Shirou.
Yeah, and that would definitely get him on Rider's good side, particularly once Sakura shows up and makes it clear she can't kill him. Anything that needles him and makes him feel shitty is good to her.