Yeah, this is nonsense. RAW, no one makes the Fortitude save: the target of the spell is an object, and objects only have to save against spells that note “(object)” in the saving throw line.
Looking at precedents, we have magic weapon, which has “Save: Will (harmless, object),” suggesting that maybe it’s common for weapon-enhancing spells to allow the weapon (or its wielder) the option of resisting it if they so choose. Maybe that’s what they were going for? Fortitude is a weird choice for that, though, and they definitely needed that “(harmless, object)” for it to work.
To have whoever is attacked with the weapon save, it really needs to say that. Actually, almost all spells that force a save from anyone spell it out, even when it just is the target of the spell. Usually, the save line is just to help you tell at a glance whether the spell is appropriate for a given target or not. Though there are exceptions—like that magic weapon above. But still, that’s very much for the weapon saving, not whoever’s hit with it.
Instead, what splinter spell resistance says is that the target just loses SR—no if’s, and’s, or but’s. Properly speaking, this also says no one makes a save.
And honestly, a save on every hit is questionable game design. It makes for a very weak spell, and it also just adds a ton of extra rolling to the game, wasting time. Balance and smooth gameplay again say no to having any save involved here.
I do not know what the author intended. I think it’s safe to say they didn’t intend to write a spell that indicates a saving throw that no one will ever make, but beyond that, it could go either way. Most likely, this happened in the editing process: someone decided the spell needed to lose, or gain, a saving throw, and then that save was removed or added incompletely. But we don’t really know what the intent was. Remember that Pathfinder mechanical material is primarily written by underpaid¹ freelancers with the bare minimum of editorial oversight, on a blistering schedule. These things happen.
But it is clear, to me, how to rule on this for the sake of the best game: splinter spell resistance is a Save: None spell. Or maybe follow the lead of magic weapon, and change it to Save: Fortitude (harmless, object), in case for some reason the weapon (or weapon’s wielder) doesn’t want splinter spell resistance (or, more realistically, doesn’t trust you and doesn’t know what spell you’re attempting to cast). Though honestly at that point I’d probably change it to Will like the rest of those kinds of things; makes a lot more sense to me.
- This is a critique of Paizo, but not as strong a critique as it might sound. Paizo definitely leveraged their size/visibility as an excuse to pay less—as did Wizard of the Coast—but ultimately the real reason these authors are underpaid is because there is simply very little money in the RPG market to begin with. Properly writing RPG material, testing it, iterating on it, it takes incredible amounts of time, and there just aren’t enough people to sell the result to. Pathfinder and D&D turn a profit, probably, but we know it isn’t much of one, even at their party rates. Also, for the record, I have been out of the scene for a bit, so I don’t know what their rates currently look like. Since this is a PF1e question, though, my experience is relevant to that.