So after looking at the material in Sentinel Tactics it is at least clear Dr Blake is not Ra currently. Whomever is Ra now appears to be either a kid, fanboy, or both based on the reaction to seeing Legacy. The Ra persona seems to have some or maybe all memory of what happened while Dr Blake was actively Ra
Mostly, this just leaves me with three questions. What happened to Dr Blake? Who is this new Ra? ( someone we've seen before or a new character altogether) Where did this new Ra find the staff so he could take on those powers? ( knowing the answer to this might answer the first two questions)
Looking at the The Staff of Ra card in SotM vs ST it doesn't seem like it is the same staff. The staff in SotM has a disk behind the red gem that isn't there in the ST version. The ST staff looks more Phoenix or at least bird like at the top compared to the SotM version.
I think whoever it is, the staff popped into existence near or in front of them, bestowing the power of Ra. If the original Ra vanished in a reality/ time-space event then it would make sense that an artifact like the Staff would find it's way to the next "owner"
Why this kid at this time? If we assume he doesn't do much before meeting up with the FV in the scenario then my guess is it is somehow related to the hulking "anubis" figure suddenly showing up. Either the kid was nearby when Anubis came a calling or he followed the staff when it appeared to the kid.
Interestingly, the text for new Ra reminds me of the Blue Beetle character from Young Justice
Dr Blake got turned into Ra when he found the staff so I don't find it too surprising that it showed up again even with Dr Blake missing. Makes me wonder if the final event in the SotM story will delve into what happens to Dr Blake.
If you read the back of the Ra Card in Tactics, it says that there is a different component - but "he still knows the heroes well and fights along side them with as much as much power as ever. But what happened to im in all these years."
"This was not a burial chamber for a pharaoh, but for a hero. Many heroes, in fact. Unbeknown to modern man, the stories of the Egyptian Sun God, Ra, came from the stories of various men who held that staff, each passing it off to a new hero when defeated."
So it there is precedence for Ra not being the same hero through out his "life", and if it can only be passed on on defeat... poor Blake.
Considering the excitable and somewhat starry-eyed conduct of the new Ra it seems like he might actually be a kiddo.
This is an instance where I'm actually comfortable speculating that (if this new Ra is a previously seen character, of course) this Ra may very well be Rook City's own Thiago (the Potential Side-Kick Victim from Spite's Deck).