As such, it's quite possible that P5D.jp and P5U.jp are for Persona 5: Dancing All Night and Persona 5 Arena Ultimax, respectively.
As more and more learn about the social Atlus RPG style through Persona 5, the greater chances the company has at keeping the ball rolling. Since the game is already enormously popular, the possibility of spin-offs like the Persona 4 Arena games and Persona 4: Dancing All Night might have a similar amount of success with Persona 5.
With so many wonderful games already released in 2017, it may seem unlikely for Persona 5 to stand out as the best - especially considering the caliber of titles like Horizon Zero Dawn and The Legend of Zelda: Breath of the Wild. What about some Persona 5 Arena?
Taking into consideration Atlus' history with "Persona 4" spinoff games, it has been speculated that the recently registered domain names are a clue to potential titles under the fifth main "Persona" entry. They posted their findings on Twitter, noting that some of these websites list Persona or are likely related to the series.
As reported by Persona Central, several other domain names were registered, including P5AG.jp, P5R.jp, Persona-Dance.jp, PQ2.jp, Persona8.jp, Persona9.jp and Persona10.jp. Other games, such as "Persona 3" and "Persona 4", were previously located in small town settings.