Tepeu initially infiltrates the headquarters of the darkness, Arkela Palace, to release the legendary Guardian of the Kingdom: The Majin. Since his forest home is displaying early signs of being corrupted by darkness, including the water turning undrinkable, he believes that freeing the Majin and restoring him to power is the only way humanity is going to survive the growing catastrophe.
Brash and headstrong, he is almost killed by the invincible soldiers of the darkness but fortunately runs into the Majin and is able to free it. Befriending the Majin with his kindness, he wields a spike used to imprison the Majin that has absorbed some of the Majin's power during its confinement to defeat the darkness alongside the Guardian.
He is apparently the spitting image of the first King of Qumarkaj, Tepeu, which is why the Majin names him such. Previously, he had no name, as he was raised by the animals of the forest and was simply referred to as "human" by them.
Tepeu is a moderately competent fighter, able to wield the "spike of sealing" both like a club and a spear. Generally, though, when alone, it is best to sneak around enemies than attempt to fight them directly. He is able to instantly kill weaker soldiers of the darkness by backstabbing them, as long as they are unaware of his presence. Tepeu grows in strength by collecting life shards, which are dropped by enemies and found in chests. Each time he levels up, he gains a little more health and hits a little harder in combat.
When fighting, he uses his relatively weak chain attacks to increase the Majin's magical power: Once the Majin has enough power, he can invoke one of his elemental attacks which render any enemies hit by them defenseless and open to combination attacks. If Tepeu falls in combat, the Majin can revive him. The Majin can also fully heal Tepeu at any time if the player stands in front of him. Should Tepeu be defeated without the Majin around, or if the Majin himself falls, it is implied by the Game Over screen that the darkness has completely overtaken Tepeu, turning him into yet another soldier of darkness. This is an early hint towards the true identity of the darkness entities.