Imhotep and Kharis are brothers
Both were sons from the same Pharaoh (Amenophis III) and got cursed. Also, Ankhesenamun and Ananka were sisters. If the Karnak priests give Kharis more than nine Tana tea leafs, he will not became a mindless killer monster...
- He will obtain his memories of his past life. All of them. And while the Tana will made him stronger, invulnerable and immortal, they will restore his young self. And he will destroy those cult that used him for millenia as a mindless slave. With Kharis being in his mortal life a Prince of the Royal Palace, it's obvious that he will not be happy.
If the story is the same, Akhenaten, son of Amenophis III, tried to kill the ancient egyptian politheist pantheon in part for the curses from his brothers Imhotep and Kharis.
Because they were cursed as mummies. Also, the Karnak cult used Kharis to kill people. Horrorized, Akhenaten hated the ancient egyptian gods, and put the monotheist Aten new cult.Kharis is an alternate universe version of Imhotep.
Similar to the theory about Son of Dracula, Kharis is Imhotep from another universe. That can explain their very similar stories. This is more or less a remake from The Mummy (1932). With Imhotep being absolutely dead and turned into skeletal remains, it's almost impossible bring him back. But instead of a godlike smart sorcerer as Imhotep, they reimagined The Mummy as a mute brute undead.