Quote from cyberium_neo »"Perhaps some familiar faces still reside on the Plane, remembering him after all this time . . . or even carrying on his family name."
That means Satoru may simply be someone who borrowed Umezawa's name to reform the Hyozan Reckoners, consider Toshiro's true heir is on Dominaria.
*cough* Ray Skywalker.
Or Satoru can easily be a descendant of one of Toshiro's relatives.