Heirs of the Empire Reborn

Among the greatest of all the space marines are the glorious Ultramarines. As the leader of Ultramarines’ task force, Commander Mechatius was sent to planet after planet, fighting the enemies of the empire.
Commander Mechatius

Though bred to fight, Mechatius was a man with a talent for words. Before each battle fought, his words would send his battle brothers into an unshakable state of determination and focus upon the task ahead. When overwhelmed by enemies and even the staunchest of the empire’s finest wavered, his soothing voice and call to action would put steel back into their soul and inspire them to greatness.
After his first battle as commander, he carved an eye into his palm and for each fallen battle brother he let one drop of his blood fall to the ground. He then looked up on the marines around him and said; “In this soil linger the blood of our brethren. Their blood stays here forever and in defiance to any who dare oppose the empire it roars; this is imperial ground!” After every battle to come, he would again set his knife to the eye-shaped scar and for every fallen brother; a drop of blood would fall to the ground.
The fall on Corroneus Magna

Over time, Mechatius’ way with words won him respect and his task force was often used to subdue rebellion that was motivated more by greed and misguided lust for freedom than of any taint of heresy or alien influence. Often it would be enough for Mechatius to have a word with the wayward planetary governor to bring the planet back into the imperial fold. Once the crisis was resolved, the task force would be off in their strike cruisers to wherever they where needed next.
The task force was sent to subdue a rebellion on Corroneus Magna, the hive-world, capital planet of the Corroneus system, which also included the smaller but heavily industrial forge-world Corroneus Inferioris. The planetary governor had been replaced with a council of elders from the planets ancient houses. The council was not interested in bloodshed and as soon as the strike cruisers entered the system, they sent a message to them that he would receive a negotiator.
A company of the Ultramarines dropped directly onto the square in front of the planetary palace. They set up perimeter sentries and then Mechatius with his bodyguard entered the palace to talk to the governor. No matter the negotiating skills of Mechatius, the council would not yield an inch. They claimed that they had no quarrel with the Emperor; they only wished to be their own masters. Then their leader uttered those fateful words. “To show you our honest intent to remain friends of the empire, we have let you in. None of your men have been assaulted and none will be. We wish for nothing more than our freedom. If your emperor wants to make himself tyrant and take that away from us, we will not stop you.”
Mechatius cut the man down with his sword were he sat, and as the other councillors rose in horror, his bodyguard shot them down in a hail of bolter fire. Nobody calls the Emperor tyrant and lives. But something in the words of the old man had stirred something inside him. So many times had his battle brothers fought planetary governments and killed the soldiers and people of foreign worlds to keep them under the heel of the Emperor. What if the old man was right? A silent, soothing voice in the back of his head told him that he had been.
The speech

The company of Ultramarines cleared out the rest of the planetary palace and met no resistance. They set up perimeter inside and turned it into a fortress. More Ultramarines made planet-fall and joined their brethren. For a full year they stayed inside the palace. Then one morning, sporadic bolter fire was heard from inside. It set the Ultramarines on edge but as the dusk settled the calm was restored.
The next dawn Mechatius strode out onto the balcony over the square where the planetary governor had used to hold his speeches to the people. The square was filled with the people of Corroneus Magna as his amplified voice washed over them.
“People of Corroneus,” he started. “I am Mechatius. I have waged battle against the enemies of the Emperor on countless planets, bringing them back under His heel!” The people in the square shifted uncomfortably. “But the emperor is not the Empire. No, we, its people is the true foundation of the Empire, we are its heirs.” A collective gasp of shock ran through the crowd at this obvious blasphemy by this chosen of the Emperor. “He claims to be a god. No wonder the true gods have turned their wrath on him! On this day, I Mechatius, Imperator of the Heirs of the Empire Reborn, declare the Empire reborn! The Empire as it should always have been, respecting the true gods. I declare Corroneus Magna as the reborn empires capital planet, and Tzeentch as its planetary patron deity!”
The crowd stared in horror as the true extend of their peril was made evident by the final words. Before their eyes the armour of the Ultramarines commander was repainted by his battle brother using their original colour mixed with ashes and its silvery trimming replaced with bronze. Finally, the Ultramarines symbol on his shoulder pad was replaced with a bronze eye with a red drop shaped iris.
The purge

The Ultramarines had followed Mechatius almost to a man, the few who had refused had already been disposed of, their ashes used to mix in the paint for their fallen brothers armour. The planetary defence attacked the traitor marines but it was a short brutal battle as many from the defence force joined cause with the traitors.
When the dust settled, five of the ancient houses had joined sides with the traitors and they used their influence to calm the people which caused the entire system to be under the control of the Empire Reborn within a matter of days.
The growing of the Reborn Empire

Since then, the Corroneus system has been used as a base of operations and more systems has fallen under the rule of the Empire Reborn as the renegade chapter has started to expand, starting with any nearby worlds on which they spilt their blood to bring it under the Emperors heel.
The Heirs of the Empire Reborn

The renegade chapter has swelled in numbers as Mechatius uses his gift of words to sway rivalling chapters to join them. Although they see Tzeentch as their patron deity, followers of all the chaos gods are welcome.
I know it's lacking in the special character description department, but it is still a work in progress. Any feedback and corrections is welcome.