Hullo, I'm Maxim.
Fighting in many more wars than he can remember, this big ol bear has some scars to display.
I guess you probably noticed that, but, most of them are on the inside.
As anyone who has been in a war can tell you, it's frightening. But you must put it behind you and fight for your life and your honor.
Let's see...
Posttraumatic stress disorder (PTSD) is an emotional illness that that is classified as an anxiety disorder and usually develops as a result of a terribly frightening, life-threatening, or otherwise highly unsafe experience. PTSD sufferers re-experience the traumatic event or events in some way, tend to avoid places, people, or other things that remind them of the event (avoidance), and are exquisitely sensitive to normal life experiences. Although this condition has likely existed since human beings have endured trauma, PTSD has only been recognized as a formal diagnosis since 1980. However, it was called by different names as early as the American Civil War, when combat veterans were referred to as suffering from "soldier's heart".


And then, if that wasn't enough, we have Thundreus.
The:
Angry
Unstoppable
Rage Prone
Bloodthirsty
War Hungry
Pedophile
Torture Prone, Lightning elemental demon that is trapped inside Maxim's body and mind.
Maxim hates and fears Thundreus because he, in turn, hates Maxim. And so the irritable elemental spirit tried as every opportunity to make his host squirm.
For example, giving him horrible nightmares about wars, his sister, and the fact that he never learned what happened to his mother.
Maxim isn't always fighting with Thundreus though, the ol' warrior often gets rest from his other side's antics and enjoys these peaceful times thoroughly.

Another thing, Maxim will only fight if it means protecting someone from harm, or asked to join a war by a benevolent leader. If the hirer is not righteous or good, however, the tainted man will find himself ruined at the other end of Maxim's iron mallet, named Chiyo meaning "Forever".