Well now we know what Persona 5 R is. What about Persona 5 S, Persona 5 M, and Persona 5 B though? Yes, those are all domains registered by Atlus. I think S stands for Switch, B is for xBox (this would be weird), or Battle (as in a fighting game), and M will either be the PC version or something I can't even guess at.
I do want to point out its pretty common for publishers to register multiple domain names for one product because they have not yet decided on what they want to use. Letters are just an attempt to hide what the product "could" be; It could have been: "R"oyal, "S"pecial, "M"asters Degree, and "B"est and they choose Royal.