>>23351075
not especially in the show other than that emma says it can power up by harnessing the souls of people. as for WHY it can power up like that, databooks that came out afterward said that the zeta had a special psycommu system called the biosensor and it's responsible for it

there might have some notes made during the show's that vaguely allude to it since they specifically show stuff like a pink energy ray coming from kamille's head when he powered up the zeta's saber, and pink seems to be the color of choice for zeta and some of ZZ's newtype miracles