Q: In the end of the Rin route, was it Shirou that projected Rho Aias in the Shirou vs Gilgamesh fight? Or was it Archer? In "Fate/side material", it's said that it was projection magic from Archer, but in the story, there was the depiction of Shirou "pulling the shield from the hill". Does this mean that this switched to Archer's scene?

A: This has been easy to misunderstand, but the part about Archer supporting Shirou was the time before Shirou pulled out Rho Aias, before Shirou came to his realization. After Shirou's monologue about his surprise that he was still alive after taking Gil's attack, "If I survived, there must have been a reason why I survived. But that was simply something I didn't have any control over." That was the "Rho Aias" that Archer made to help Shirou in a way that wouldn't let Gilgamesh know there was someone else waiting to ambush him.

Fate/complete material III; FAQ, pg. 130