Army of the Waves

Medea Pideth Machina is the main antagonist of the Rising of Shield Hero.Medea is a goddess whose goal is to unite the eight worlds which comprise the Heroes World, which have been reduced to two by the time the story takes place, and then descend into the fused world to devour its energy and move on, presumably to do the same thing again elsewhere.

Appearance
Medea is described as being an unparalleled beauty, much like her fragments, carrying a glowing image that suits her nature as a deity.

Personality
Much like her fragments which work to sabotage the heroes and ensure her Waves of World Fusion go uninterrupted, Medea is rotten, selfish and unrepentant, Malty Melromarc herself is nothing more than a fragment of Medea and as such Medea possesses all of her memories and personality traits, only she is far worse than Malty because she has the power to back up her selfishness. She sees everything existing for her sake and inflicts betrayal purely because she loves the expression on her victim's face when their friends and family are turned against them. Similar to Malty she also immediately starts acting like she's the victim when her enemies start getting the upper hand, complaining as she's killed that so many people want her dead. She also grossly overreacts to light wounds, annihilating Ren and Motoyasu for inflicting a light cut on her wrist, it's likely she's simply not used to getting hurt at all.

Her grudge against Naofumi is personal to the extreme, after killing Motoyasu and Ren, she proceeded to erase Naofumi from the world and every divergent world and parallel timeline he ever existed in, as Ark put it, "She really, REALLY, wanted you dead man", and she was even more annoyed when he came back even from that, this time a God himself, and completely turned the tables on her.

She spared the Heroes' world for a time only because it amused her to have her underlings kill the world's inhabitants in a twisted war game, she also personally interfered whenever it looked like her army was losing, referring to it as her correcting the enemy's side's cheating. When Naofumi returned and completely turned the tables on her by giving the Heroes' side a god, she immediately tortured her subordinates to death just to laugh at their cries of betrayal before confronting the heroes herself, which even disgusted the heroes, who themselves had no sympathy for her men.

She is extremely boastful, calling her attacks with words like "ultimate", "infinite", "Faster than infinity" ect, but as Naofumi himself states when he becomes a god, it's all bullshit, her attacks are bound by finite restrictions, it's just that she's so powerful that non-gods normally wouldn't be able to notice.

Background
Medea is a member of an ancient civilisation that somehow or another gained immortality and God-like power. At an unspecific point in time she approached the Heroes' Worlds and started fusing all eight of them into a singe world so she could enter and absorb it. She has used her powers to reincarnate and brainwash several individuals into these worlds to sabotage the efforts of the heroes who oppose her while also incarnating her own fragments in positions of authority in said worlds to regulate the process.

Final Arc
After her reincarnated individuals rip open the last wave and fuse the last two Heroes' Worlds into one, she descends into the world in person to lead them. Triumphantly declaring the heroes evil for their treatment of her fragment Malty to motivate her men, she proceeds to buff her soldiers and have them attack. Seeing how ineffectual her men actually are in battle she revives the Queen of Melromarc as her puppet to lead them. The Heroes strike her with the Zero Series Weapons, inflicting a minor cut on her wrist, which infuriates her enough to obliterate Ren and Motoyasu, however Naofumi blocks her attack with his shield. She proceeds to then erase Naofumi from the world, all divergent worlds and all parallel timelines where he existed to finish him for good, accidentally getting Raphtalia in the process, and leads her army to assault the remaining heroes, led by Itsuki, for no other reason than amusement.

She revived the several of her enemy's fallen comrades, including the Granny and several of Naofumi's slaves, to toy with her foes emotions during the slaughter and stepped in whenever her men were losing, keeping the world alive just to amuse herself when she could at this point easily win. She kept this up until Naofumi and Ren returned, much to her surprise as she herself did not revive them, and forced her men to flee.

When her men have their weapons stolen by Naofumi and given to his allies(the weapons themselves actually wanted this, Naofumi only freed them from Medea's control) she attempted to steal the heroes' weapons in retaliation but was thwarted again by Naofumi. Medea recognises that her men are effectively useless at this point and kills them herself for the fun of it before facing the Allied Forces. She gloats about her victory to Naofumi and attempts to destroy the world herself, only to realise that Naofumi and Raphtalia have also become gods like her as they completely thwart her attempt and proceed to beat her to the ground. Infuriated, Medea tries to counter attack, but Naofumi and Raphtalia bind her to the world and buff their allies, reducing her to a mere Boss Character and allowing their comrades the chance to attack her themselves to vent their own feelings of frustration and hatred. Medea finally loses it and tries to erase everyone from existence as she tried to do to Naofumi before, only for him to reflect the attack back at her, she tries to reason that her real body isn't even in the Heroes World and she thus can't die, only for Naofumi to remind her of what she herself declared when she killed him before: that this attack kills you in every world, parallel timeline and alternate universe in which the victim ever existed. Utterly unable to cancel her own attack, Medea is destroyed and her power is taken by Naofumi to restore the Heroes' World and undo the damage she caused.

In effect, the only reason anyone even remembers her is because her energy was used to fix the world and is the only part of her that still exists at all, rendering her nothing but the lingering memory of a person who technically never even existed to begin with.

Powers and Abilities
Medea has access to three major know magics, the first one is called Concept Magic, which allows her to basically kill anyone just by envisioning them dead, and the second one is a form of temporial magic that allows her to kill a person in any world, parallel world and divergent timeline where they have ever existed in, effectively erasing them from all of existence(she herself was not immune to the latter). The third magic she's seen using most often allows her to reincarnate, revive and manipulate the dead, as Naofumi himself states while contemplating that becoming a god also gave him this power, it's not without its failings as the revived individual can suffer irreversible damage to their soul if the user isn't thorough, Medea however uses this power constantly on her men and the fallen amongst her enemies with absolutely no regard for these risks, she simply doesn't care that their souls themselves are being destroyed by her actions. She has the ability to steal and enslave the weapons of the Heroes and can even bestow powers unto her own men, but the efforts of another god, as Naofumi proved, can completely undermine the former and free the weapons. Her knowledge of other world's magics even gave her some spells that just seem like formless energy, and she has one power called "Infinity Destroyer" which supposedly kills all the heroes, steals their weapons and destroys the world all at once, but none of this could even bother the deified Naofumi, who completely nullified them all. She is also capable of using lightning based magic which affects the entire battlefield, however this magic doesn't instantly kill her targets, it burns them alive until they're nothing but ashes. She also wields a sword, which she claims "has infinite speed and is the infinite, ultimate, strongest sword technique that nobody can see through," when in reality she's just sending her sword back in time to attack before she even swings it and she is completely out performed by the deified Raphtalia in this regard since her attacks can ignore the concept of time outright.