Yes, I know, I have too much time on my hands. This is my 4th Demigod Idea. I figured I'd round it out, now I have one of each type for each side.

Demigod: Ao & Ona (Assassin)

Appearance: A headless, tattooed giant about half the size of rook holding two sickly, young children, a boy and girl, one in a 'seat' upon his shoulders, and one cradled in his left arm. The children are dressed in rags.In his right arm he carries a savage looking scepter or mace.

Summary: Ao & Ona; Psychic Twins in control of their massive guardian. Switching between the two, Ao & Ona go from a tough, implacable tank to a savage, unstoppable melee juggernaut. Ona is normally dominant, sitting on the juggernaut's shoulders. She uses abilities like mana sheild, meditation, and psychic lash to hold the line and attack from afar. However, Ao is much the stronger and aggressive twin, and when he takes control of the juggernaut, he becomes an engine of destruction, able to use his devastating abilities without regard for mana, though this takes it's toll on the twins' health. The trick, then, is to balance Ona's calm, methodical presence with the savage fury of Ao to take enemies off guard, without leading them into their demise.

    When the Duchess grew heavy with child, rumors flew. The Duchess was yet unmarried, and notoriously promiscuous. All the realm wondered who the father was, and the Duchess would never tell. The father himself, however, believed that he knew perfectly well. The Duchess' court mage, a wise yet vigorous man, and something of a coward, was content to keep his peace.
    At the birth of the twins, the Duchess was dismayed to find them sickly. A little boy and girl, both albinos, she named them Ao and Ona, after the cursed children of the last Gordian king. Such inauspicious names bothered the father, but still he kept his peace, and the children were thus raised in an atmosphere of cold neglect from their mother, and hidden warmth from their father, who saw them every day and yet could never reveal himself.
    The twins were always strange children. They rarely spoke aloud, and never to each other. This wasn't due to distaste, but from lack of need. The siblings seemed to always know exactly where the other was, and what they were thinking. Strange events surrounded them: Moving furniture, sudden changes in temperature, and other phenominae. They never had any trouble convincing others to do what they wanted. It soon became common knowledge that the twins had strange powers, and their father was commissioned to make wards to protect their caretakers from their influence.
    Ao and Ona were never in any danger until 10 years later, when the Duchess became pregnant once more, and gave birth to a healthy, squalling boy. Unsatisfied with Ao and Ona as her heirs, she set about planning to have them sent away and murdered. Hearing of this plot, the father came close to confronting the duchess and condemning her, but alas he was too frightened of his mistress.
    Instead, in his workshop, he began constructing a guardian that would take them far away from the Duchess and protect them ever after. A large statue of living bronze in the shape of a giant man, he spent many days toiling over it, instilling it with absolute loyalty to his children. He was in such a hurry to complete it, however, that he left out the head.
    Too soon, the Duchess set her plot into motion. Under pretense of sending the twins to visit their grandmother in the next county, she sent them into the wilderness with soldiers utterly loyal to her. Upon hearing of their departure, their father pannicked and sent his construct after them unfinished. The construct was imposing, but headless, and it knew not how to fight effectively.
    By the time the construct found them, however, it was too late. Their 'guards' had just snapped both of their necks. However, the construct was aware that they still lived. Scooping them up in it's massive arms, it turned to take them away from the bewildered guards. Suddenly, it stopped. It turned. Their colorless eyes blazing with betrayed fury, the twins had taken control of their would be savior. Placing Ao upon it's shoulders, where he sat in the hollow where it's neck would have joined it's torso. It picked up it's massive mace, and advanced on the guards, who attempted to run, but found themselves frozen in place but an unseen force.
    When the guards were dead, the twins marched their construct, which they named juggernaut, back to their home. Seething with juvenile hatred, they slaughtered the people one by one, and tore down the keep. Saving their parents for last, corralling them into the ruins of their father's workshop, they hesitated for a mere instant, seeing only a cowardly man and a bitter woman with her squalling child.
    It only lasted an instant, however, and they reminded themselves that the one had condemned them to death, and the other had been too much a coward to save them. One swipe of the juggernaut's mace ended them.
    Legends of the juggernaut and it's strange children persist to this day. Never aging, nor forgiving, the twins wander the earth in silence. For the most part, Ona keeps them hidden and solitary, but every few years Ao's blind fury takes control, and whole cities are wiped out.

Strengths: As Ona, abilities that reduce damage taken and hinder enemies.
    As Ao, powerful melee abilities that don't cost mana

Weaknesses: As Ona, dependant on mana to fuel abilities and attacks.
    As Ao, constant health drain leaves him vulnerable.

Abilities:

(Start)Psychic Switch: Transfers control of the juggernaut to the other twin. As Ona, juggernaut gains 200 armor and ranged auto attack. As Ao, juggernaut gains 100 weapon damage, melee auto attack, and loses 5% health per second. All Ao Abilities cost no mana.

(Ona)Psychic Lash: An incadescent whip of psychic energy laches out, dealing 200/300/400/500 damage to all enemies in a cone 50 feet in front of the juggernaut. Enemies are stunned for 1 second.

(Ona)Mana barrier: Toggle. The juggernaut is surrounded by a mystical barrier. 20/30/40/50% of the damage Juggernaut takes goes to mana.

(Ona)Stay And Play: All enemies within 40 feet are rooted to the spot. Rooted enemies can attack and cast, but not move. Root lasts 1/1.5/2/2.5/3 seconds.

(Ona)Multifocus: Ona's Auto attack hits up to 2/3/4 targets.

Meditation: The Twins' gain mana regeneration. +20/30/40/50 Mana per second.

Enhanced Mana Barrier: One point skill at the end of Mana Barrier tree. Mana barrier also adds 500 armor.

(Ao)Tantrum: 5 second cooldown. The Juggernaut flails wildly with his mace, smashing it around him randomly three times for 200/400/600 damage. 4th point adds two more attacks.

(Ao)Give Us A Hug!: 12 second Juggernaut captures an enemy in a crushing bear hug, stunning himself and an enemy for 3 seconds and dealing 200/300/400 damage per second.

(Ao)Get Away From Us!: 10 second cooldown. The Juggernaut swings his massive mace in an arc, dealing 300/500/700/900 damage to all enemies in a 180 degree arc in front of him and knocking them back.

(Ao)Palapable Fury: Ao's fury is so great that every 3 seconds a wave of pure hate eminates from him, dealing 20/40/60/80/100 damage to everyone within 30 feet. Only active with Ao.

Very nice idea. The only conflict I can find is that there are two of them and only ‘one’ will ascend that wins the tournament… but then I got thinking. A man is a body, soul and spirit. Three parts make up a person and there are three that make up your Demigod, the Juggernaut being the body and Ao and Ona being the soul and spirit. So it could really be ‘one’ singular entity.