Mobile-Fortress Destroyer

"It is an ancient weapon, and wherever it rampages through not even the grass remains."

- Darkness explaining the threat of the Destroyer.

The Mobile-Fortress Destroyer, often shortened to the Destroyer, was a major antagonist from the light novel series, Konosuba: God's Blessing on this Wonderful World!, as well as its manga and anime adaptions. It also serves as the main antagonist of Isekai Quartet.

The Destroyer was an ancient and powerful robot hellbent on the destruction of human civilization, which served as a major antagonist towards the beginning of the series. It was eventually defeated and destroyed by the combined efforts of Kazuma's party and Wiz.

Creation
The inventor of the Mobile-Fortress Destroyer was a lay-about from Japan, who came under the service of the advanced civilization Norse. Norse wanted the inventor to create an incredibly powerful weapon which could be used against their enemies. The inventor, not wanting to be executed, agreed to build the weapon.

Eventually the Mobile-Fortress Destroyer malfunctioned, and, because the inventor forgot to make an off-switch, was able to destroy the kingdom of Norse in it entirety. After destroying Norse, the Destroyer continued rampaging for centuries, eradicating any civilization that came into its path.

Destruction
Centuries after destroying Norse, the Mobile-Fortress Destroyer set its sights on the town of Axel, which was the starting point for most adventurers in the kingdom of Belzerg. Unfortunately for the Destroyer, a young adventurer named Satou Kazuma and his party resided in Axel, who came up with a plan to annihilate the Destroyer.

When the Destroyer came into sight of the town, Kazuma's party priest Aqua, unleashed a powerful dispel spell which broke the magical barrier surrounding the Destroyer. With its shield down, the Destroyer was left defenseless against powerful spells.

Taking the opportunity presented by Aqua, Kazuma's arch-mage Megumin and the undead lich Wiz unleashed powerful Explosion magic on the Destroyer, completely deactivating it.

Self-Destruct Sequence
Upon being defeated, the Destroyer began its self-destruct sequence, intending to wipe out the town of Axel. However, Kazuma led an incursion into the Destroyer in an attempt to halt the self-destruct sequence. Eventually Kazuma was able to locate the coronatite power source, and with the help of Wiz's teleportation spell, was able to expunge the coronatite to a uninhabited area.

However, the coronatite was not the only problem for Kazuma and the adventurers of Axel, as the hull of the Destroyer began rising in pressure. As Wiz noted, if the Destroyer's pressure was risen too high and it detonated, it might still destroy Axel. Kazuma was able to quickly come up with a solution, having Megumin use her Explosion magic to obliterate the Destroyer's body before its pressure could rise too high. Fortunately this worked, and the threat of the Destroyer was vanquished by Megumin for good.