Warhammer: Guilliman Returns? Ultraman!

(The Emperor will awaken midway through the story.) “Roboute Guilliman, I have seen your courage. You faced a mighty foe without regard for your own safety, seeking to save humanity through your own strength. Your bravery moves me.” “I give you my life. Together, we will strive to defend peace across the galaxy and freedom for humanity.” “You are now an Ultraman.” It is the forty-first millennium of humanity. Abaddon the Despoiler, Chaos Warmaster, launched the Thirteenth Black Crusade, destroying the fortress world of Cadia and tearing open the Great Rift across the galaxy. Countless powerful monsters and aliens entered their galaxy through the Great Rift. These dangerous xenos joined the war and its orgy of slaughter. The Astronomican's light had gone out on Terra. Xenos, daemons, and traitors rampaged across the galaxy as people cried out in despair, as if the endless night of old had descended once more. But the Cicatrix Maledictum brought more than enemies. It brought hope, too. A vast planet made of green crystal appeared out of nowhere in the Ultramar Sector. The Imperials on nearby planets called it the “Land of Light” and reported seeing a gigantic alien race moving across its surface. The Primarch Roboute Guilliman returned in the form of a silver giant, vowing to destroy the xenos and traitors and restore humanity's former glory. Even the Master of Mankind was slowly awakening from his slumber, seeking to win over these alien allies from another universe, known as “Ultramen,” for one final struggle against the Dark Gods. “Roboute Guilliman, you are both light and human. Go and do what you believe is right.”