How he became a Yami without a Millenium item is due to long term exposure to the items. Which if ya want lore on that lemme know

Previous known as Amenkno as well as having its deck changed. His Ka back in the ancient times was Cerulean Sacred Phoenix of Nephthys so he would be playing a Nephthys deck now. He is the Yami to Tamotsu whose redesign will come out later.