akikan40
It would be amazing if Ajuka figured out that Riser has a system and sneakily removes if from Riser without him noticing. Because Riser doesn't think of the system until the system pops up.
Since Riser has only seen the anime, then he shouldn't know that the Sephiroth Graal could revive Sirzechs and reveal the truth of his murder. Unless he finds out this information when he becomes a Maou or investigates since, I don't think that the information about these Sacred Gear is impossible to find with several users who have used it among the humans.