A very unusual crossover. I can't say much because it only has one chapter, but so far you've put the world and Shirou's situation very well.
Bonus for making an adaptation to the summoning ritual chant.

Looks good so far, I look forward to reading more.

Good ole Zelretch messing with Shirou again. Now did StarSwirl actually have anything to do with it is the real question.

He prepared his married blades Kanshou and Bakuya once more as he assumed Archer’s preferred sword stance. Leaving obvious holes in his guard in order to lead his opponent to striking them, in a way allowing him to predict his opponent’s attacks. Of course this was assuming he was fast enough to parry the attacks aimed at him.

IIRC this stance was actually only used once against Lancer in a specific situation, given it would be effective in that scenario, and is not necessarily the preferred stance of archer, just another stance, like any other in his toolbox of swords.

Unfortunately, I can't find the citations for this as I would essentially have to go over every fight archer was in and run comparisons