Intro: This is probably the most amusing pairing I have ever seen. Even Lancer approves! And that's all that matters!

Proof: Aside from Lancer, these two have a lot more proof. In Unlimited Blade Works, it is canon, as the two have admitted it. The thing is, Rin makes it adorably obvious, being that's she's freaking tsundere.

What I think: Out of the three people fans ship Shirou with (the other two being Saber and Sakura), I feel like this is the one that makes the most sense. Even still, if fans don't like this one, there's still the other two versions of Fate/Stay Night to keep them satisfied.