Board Thread:Questions and Answers/@comment-3076045-20171210124631/@comment-1192086-20171210231919

Since Archer as a Heroic Spirit is removed from the time axis, any path that shirou takes will not affect his existence. Thus, while shirou and archer share the same past and identity, they can be thought as seperate existences in a sense. But, whether or not Shirou becomes a guardian hinges on if he gives into despair and forms a contract with Alaya or not. That's two cents about it at least.