(1)

Cole explained "The Call' when the stone would glow when he is needed, flames coming from the stone in his possession wherever it could be. 

(2)

You were trying to help him by using your own means to affect the stone.  But you only made things much worse. The magic interfered with the stone's protections, allowing the 'mentor' inside the stone to have more freedom to manipulate Cole's body.  

(3)

It was an  attack aimed at the core of his armor, where the stone resided in. It reacted violently, an eruption of hellfire that destroyed the area around Cole leaving him the only person unscathed. 

(4)

                            The magic used on the stone  forced Cole to end up in the past, a moment in time when one of the older Rogue Sun's was active.  You were trying to find a way to follow him back though time to that point.

(5)

He was forced to wrestle with the spirits of the other Rogue Suns, dealing with their souls and eventually emerging different after destroying one of them. Possibly burning brighter, absorbing their energy, and making the sun stone unstable. The black armor molting into a shining white. Cole was just as confused as you were... 

(6)

(For those whose ocs exist in another era or history, period pieces, fantasy or mystical)  

The boy who appeared was strange he may have had the same armor but he did not live up to the reputation of the Rogue Sun.  He spoke oddly and often cut himself off in some sentences.   Then he revealed the truth \some of the truth .   That he was another 'Rogue Sun', someone in the armor who ended up by accident, or the Rogue Sun of another time.  Doing his best not to tell you of the future. 

The monster disappeared soon after the explosion was felt, and it seemed like the hero of the realm had appeared in the nick of time. But he appeared reluctant. 

(Or make your own for this starter I wouldn't mind messing around in the past.)