I’ve been wracking my brain, and I think this is a classic case of a phrase turning into a rumor without a solid source. There's no single 'Sword Emperor' character in widely known fantasy that commands a specific set of legendary swords as a core trait, at least not one that's a universal reference.
You might be thinking of a trope, like a king who collects mythical blades, or perhaps a specific character from a novel or game? The phrase feels like it could belong to a progression fantasy or LitRPG setting, where a protagonist earns a title like 'Sword Emperor' and gathers artifacts. Without a specific book title, it’s tough to pin down. I’ve seen similar discussions pop up around cultivation stories where the lead ascends to some grand martial title.
My guess is someone heard a cool-sounding phrase from a niche series and it’s taken on a life of its own. If you remember where you saw it, that’d help narrow it down immensely. Otherwise, we’re all just guessing at shadows.