I've had this in the back of mind since 1992. Back then, I created a kind of LARPG with a friend of mine based on feudal Japan. We called Komoto-Arterian (yes, I understand that is more Chinese) and dealt with two wandering (what else) shinobi who broke their ranks and are now hunted by their clan but still try to help out others on their way.
They also spar and fight between themselves.

Oh, yes, they're also chasing down a cursed sword their mother once owned.

Anyway, over the years I thought of changing the premise to focus more on the sword an a time loop that revolves around it. In my version, a young adult male on vacation attends a gallery showing of artifacts from Japan and his eyes become transfixed on the hilt of the blade as it has strange writing--writing that looks like half of his name--from the top part. He shrugs it off as a cool coincidence and takes a picture of the sword.

He looks at the picture and swears he sees the image of someone in it...someone who looks like him, but maybe not...
The next day he comes back to the gallery, goes past the ropes and grabs the sword.

He sees the full image of the girl--in a mirror--as he is now the girl, and she's no longer in 2018.

I plan to have be an eight chapter, novelette or I may screenplay it in hope to have it storyboard, one day.
Music and style by Azuma