@t1clever when Shinra went back in time, his doppelgänger took over his body, so the Shinra we knew was "sleeping" whilst his Adolla version took over his body (why? we don't know, only that out Adollan counterpart want to take over). Shinra's doppelgänger dyed his hair blonde and other body modifications because doppelgängers behave in a way other people think the original is, for instance Shinra was always called "demon" so his doppelgänger was more of a rebellious character. And from that we can assume that Iris calm behaviour might be how people used to see Amaterasu/1st Pillar, as a calm person - besides, unlike Shinra, it seems like somehow both Iris and Amaterasu can coexist with different bodies.