The electromagnetic control is sorely derived from Magnet Release and Lightning Release, by combining the two such an ability becomes possible. However, without refined chakra control and proper ratio of combination of the two this is not possible. This technique works on the principle of how electric currents interact with magnetic fields. It the magnetism, so produced when electrical surge or minimal current is passed through an magnetized object (which ofcourse has been magnetised with his magnet release before hand), at basic levels this also requires a metal but later on with mastery Hotaru was able to do the same with the bodily iron contents of an average shinobi.