@Jon-Mitchell
I have another theory. Eizo's notoriety has reached the empire. Helen's two "lightning blade" swords were payment along with a cart filled with his elite weapons reached the empire as "payment" for a troublesome area. That is why Marius was notified and the reason why Eizo was involved. The Epilogue goes on to say that the emperor knew about the rebellion but lacked forces to keep it. Rebellion forces were the ones that captured Helen. It looked like they had outside support from the kingdom side (key question is who). They are right. A dead body of a famous mercenary would lead to questions if her body was found in the kingdom side (especially if they knew her lineage). If her body was found during an Empire rebellion, then that would be a different matter.
Helen is the Margrave's illegitimate daughter. Figured since he had an unusual interest in her safety, red hair, and prowess in the battlefield. I would not be surprised if he was giving her jobs, giving her opportunities, directing her activities in the shadows, etc. I view magic as an equalizer (women and men can become powerful, but most nobles will use their bloodline as pawns [doesn't matter the gender]).
I would not be surprised that the "elder" was one of the guards that Eizo helped with their swords and noticed he was killing rebellion troops.
But here is the key thing. Eizo is leveling his skills and is getting stronger along with greater access to mystical metals!