Zaldias serves as the primary antagonist and Demon Lord masterminding the demon invasion threatening the world. Originally defeated and sealed away by the past incarnation of Matthias, Zaldias possesses near-immortality, regenerating from any injury; only complete annihilation ensures his permanent defeat.

He orchestrates the demon invasion from the shadows, manipulating events and individuals towards his goal of humanity's destruction. Lurie acts as his key pawn, unknowingly manipulated to weaken the barriers containing Zaldias and enable his resurrection.

Zaldias's ultimate scheme requires possessing Lurie's body to fully manifest physically. Successful possession grants him immense demonic power, surpassing all other demons. This state manifests a distinctive third eye upon his forehead.

His physical presence radiates dark, demonic energy and a menacing aura. Zaldias exhibits extreme arrogance, viewing humans as utterly insignificant vermin and expressing profound contempt for their existence. He is ruthless, actively reveling in destruction and the suffering he causes.

The culmination unfolds at the demon castle, where Zaldias, now possessing Lurie, confronts Matthias and his companions. Relying on his overwhelming power and regenerative immortality, Zaldias engages them in a fierce final battle.

Matthias, drawing on knowledge from his past life and the specific vulnerability within Zaldias's immortality, devises a strategy. The battle concludes with Matthias successfully destroying Zaldias's core, achieving the necessary permanent annihilation to end the Demon Lord's threat.