UBW’s epilogue drops us in London two years after the end of the Holy Grail War, with Shirou tagging alongside Rin as her pupil at a Hogwarts-like magical college. It would also seem they’re living together, and are quite happy about it.
After we’re shown some glimpses of their new life—home-cooked breakfast for Rin (still not a fan of the morning), an English love rival who spars with Rin in a kind of magical MMA bout; Shirou nursing Rin’s wounds after her defeat.
The couple takes a day trip to Glastonbury to visit King Arthur’s tomb, a trip Rin plans so Shirou can properly say goodbye to Saber. It’s a nice touch, and the English countryside and ruins are lushly rendered.
While on the bus ride home, with Rin asleep on his shoulder, Shirou reflects on the events that got him here to this point, by her side. A month after the war, Rin tells him of her plans to move to London and attend the mage’s university, inviting him to come along; an invitation he gladly accepts. Rin’s primary postwar goal is to make the man she loves happy, which means keeping him by her side.
Back in the present, in an encounter I’m sure had more resonance for those more familiar with the franchise, a tall, stern man questions why Shirou is there, and remarks that it’s a “small world” when he hears of Shirou’s desire to be a HoJ. My guess is this guy knew Kiritsugu.
Shirou has been invited to join the Mages Association and eventually Clock Tower, but he declines. Rin isn’t particularly surprised, but is more than willing to follow him as they see the world they saved. Lots of great loving smiles from Rin in this epilogue.
Shirou and Rin’s indications, along with the post-credits sequence, suggest Shirou will never be able to escape the same path as Archer, but until then, he and Rin are going to have as many good times as they can. When the time comes, she hopes her positive influence in his life will enable him to move a little further forward and get “the right ending.”