The power of the Grail, now in the hands of the Laḫmu, has transformed the Persian Gulf into the Chaos Tide. Any living thing that touches this sea is instantly mutated into a Demonic Beast.

As the Chaos Tide advances toward Uruk, Fujimaru and company form a desperate plan to destroy Tiamat as a last-ditch effort to save the city.

Tiamat falls into the underworld, but there, she transforms into one of the Evils of Humanity: Beast II. Hassan-i Sabbah, the first Old Man of the Mountain, intervenes, using his power as Grand Assassin to deprive Beast II of her immortality.