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 discover 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, Damian greatly appreciates it. He often competes with Achetto to see who can get the most favour with Mira. Compared to Achetto, he's more level-headed and doesn't put himself into risky situations.
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 something, discovering a Rebel facility where Emma sends the Crablops Type-Lower against him. He eventually destroys the Crablops Type-Lower and pledges his allegiance to Mira for giving him new life.
He's later paired with Achetto in capturing the Cyclobster, though the success of the operation remains unknown.
Damian later partakes in a United Front operation. During the battle, he spots a woman that grabs his attention; despite being enemies, he temporarily disobeys orders to put him in danger, but also makes sure that she can see him so that he can impress her with his movements, which was successful, as the woman commented on how mysterious, yet charming he was. After the operation, he finds Achetto writing a report and discovers that she is reporting him for endangering the operation, though he claims that he did so for good reason.
While performing an experiment with Achetto on an unnamed cultist, he senses another presence approaching them. Though he initially puts up a fight, he realizes they are outmached and sends Achetto away to call Mira. When she leaves, he tosses his sword and shrugs, asking the presence to leave as though he'd gladly die for Mira, he would rather not die in an "accident". The presence agrees to leave, although it is sucked away as it attempts to leave.
When the Golden Ptolemaic Gigant goes out on a rampage against the Rebel Army, Damian is seen idling around. Upon noticing numerous soldiers of various affiliations converging on their position, he learns from the master believer that Beatriz has called them to support her, and he decides to partake in the battle. He soon encounters and fights Beatriz, taking out her bodyguards doing so. He asks her to surrender, noting that her hands are almost at their breaking point, but she refuses, calling him a narcissist and fires a high-powered beam which surprises him. Damian survives the attack and returns to Mira, lamenting his failure, but Mira reassures him since the battle was insignificant and gives him a new assignment.
After Mira returns with new powers and begins a spell to eradicate their enemies from the world, Damian is fighting off Elena and Licht. Despite putting up a good fight, he's eventually bested by them due as their hope overwhelms him.
He later recovers and goes on another mission, where he is dragged into the border between life and death. Greeting him is a mysterious witch, a large number of demons and the undead, and Ichima. Ichima explains to him that the otherworldly creatures will drag him to death. Damian, refusing to accept this, somehow manages to manifest Mira's darkness to empower himself and clear the area of enemies. He later returns to base with the witch and boasts his newfound powers to Achetto, causing her and the witch to try to kill him, much to his worry.
Damian makes an appearance in "The Tale of Ω" where he accompanies Mira to an island to intercept Red and his group. He battles Aileen and her pirates and easily defeats them with his powers, before reuniting with Mira and Achetto. Damian and Achetto soon squabble over who had the better fight, but Mira orders them to capture Licht and Elena to gain more favour. However, the pair escape before they can capture them.
Mira later takes him, Achetto and Sally to revive Ptolemaios. Due to the urgency of the ritual, Mira takes Damian with him, prompting Sally to challenge him as she wants to accompany him. Damian accepts her request, but Mira stops the both of them as they have no time. After Caroline sets off an explosion that destroys much of the base following her defeat, Damian finds Mira and returns her to the ritual site, where he witnesses both Ptolemaios and Mira reborn.