Disclaimer: Idea i've had for a while now, pretty generic as far as ideas go tbh.
Also, for the couple of people that have asked if i'm going to do anything with these prompts/ideas and those of you who have followed/faved some of my prompts, I don't plan on doing anything with these, mostly because of the fact that i'm bad at writing.
When Ritsuka Fujimaru closes his eyes, he doesn't see the lives of his Servants flash through his eyes mind, nor does he dream of the horrors he's seen since Singularity F all those "Years" ago. No, he dreams of Woods shrouded in fog, a little girl eternally playing the one she loves favorite song on her precious Ocarina, a blonde haired young woman who radiates sadness and longing, and a Sword that banishes the Darkness.
Nitty Gritty Time.
This takes place several hundred years after Breath of The Wild and a week after Lostbelt 4.
If it wasn't already obvious, Ritsuka is the reincarnation of Link, whose soul somehow(CoughGanonCough) made it into the Fate/Grand Order timeline.
Ritsuka is having these dreams because Fi/The Master Sword are calling him.
Fi will be showing up as a companion for the duration of Ritsuka's time in Hyrule, it'll just take a little while for her to wake up completely.
Ritsuka does eventually find his way into Hyrule, but don't expect it to be a simple "He stumbled upon a portal to Hyrule" thing, there are quite a few Goddesses vying for his affections and they would do virtually anything to keep him from being shackled to Demises Cycle of Death and Reincarnation.
In terms of holiness, the Master Sword would be somewhere between Caliburn and Excalibur, but wouldn't be nearly as strong as either simply because of the fact that Caliburn and Excalibur are Noble Phantasms and the Master Sword isn't.
When he does manage to find his way into Hyrule, debating on whether or not Ritsuka will be taking one or two Servants with him, i'm thinking Archer EMIYA and maybe Mashu, if that.
Previous incarnations of Link will show up periodically in Ritsuka's dreams shortly after Ritsuka obtains the Master Sword in order for them to teach him how to use it and to reteach his original fighting style.
And that's all I could come up with, BoTW showed us what a damaged Link is like and ever since then i've been wondering how an even more damaged Link would go about saving Hyrule, and this one still has all of his memories to boot.