Damian is a new character introduced in Metal Slug Attack.
Prior to joining the Ptolemaic Army, Damian was a well known swordsman who was appropriately called the "King of Blades". However, he would eventually take a grievous wound during one of his battles. This would cause him to suffer from short-term depression.
Mira would eventually stumble onto him during one of her missions and recognized the swordsman. She promised him the ability to regain his swordsmanship, and he eagerly took the offer. Like Simon, Damian would be experimented on with unknown powers. His left eye would be covered by a metallic plate and his sword was also modified. The hilt was replaced with a gem which seems to be responsible for empowering him. His swordsmanship was restored and he obtained some magical abilities following the experiment.
While Simon seems to be rather indifferent to the experimentation, Damien greatly appreciates it.
First appearing in "Sword of Allegiance", his past is revealed along with how he came to his current state. Not sure of how to repay Mira, he decides to destroy the Crablops Type-Lower. He eventually destroys the Crablops Type-Lower and pledges his allegiance to Mira for giving him new life.