Fate Grand Order's Demonic Blacksmith (Not a story, it is an idea for one)

As we all have found, Emiya Shirou is a descendant of Sengo/Senji Muramasa and often becomes his vessel in FGO with Shirou being the controller in various fanfics. But what if he was summoned in FGO but with Muramasa being the controller but give him the usual powers they would receive. What twists would occur when he meets his vessel's past friends, family, and the woman who shirou harbored slight romantic feelings for?
This was kind of inspired by a fanfic I read (I can't find it again but it's on Fanfiction.net but if you find it then you know who the credit of that story goes to) and what happened was Emiya Shirou (merged with Muramasa) was summoned to Chaldea but due to an error he lost his memories but kept his skills, so he doesn't remember Artoria and others also Artoria is the Ship in the story. Sorry I can't properly name the author of that story since I can't find it again.