Even though Sasaki's droll corporate life is constantly filled with work, it leaves him tired and unfulfilled at the end of every day. In search of some companionship to fill the emptiness in his life, he visits a pet shop on a whim, not realizing he's about to change his life forever. After settling on an adorable bird and bringing it home...his new roommate reveals that it's actually an incredible sage from another world who promptly bestows Sasaki with supernatural powers as well as the ability to cross between worlds. All Sasaki wants to do is use these newfound powers to live in peace and comfort, but there are more than a few colorful characters who might get in the way of that...

Rud is a tank of the Hero's Party and is said to have the highest defense ever in history. The party often does labyrinth raids, but to Rud, it means more than just a raid. To cure his beloved sister's illness, he is in search for the wish-granting treasure that might be hidden in those labyrinths. But one day, the arrogant hero kicks him from the party after an unsuccessful raid attempt, blaming it on his skills whose effects he is still unaware of. Without nowhere else to go and nothing to do, he decides to return to his hometown, where his sister is waiting. On his way there, he saves a girl who was being attacked by a monster. Unexpectedly, this girl has an extremely rare skill called "Appraisal." Thanks to her skill, Rud is able to discover the truth behind his unknown skills, which turn out to be very powerful skills. With a defense of 9999 and powerful skills, thus begins the adventure of the strongest tank, Rud!

Outside the magical barriers lies a world overrun by fiery beasts known as Flame Demons, and the only ones who can protect humanity are the Fire Hunters. In the dark woods where the beasts roam is where Touko, a young villager, is rescued from attack by one of these skilled trackers, Koushi. But their meeting was no accident, and a new destiny begins.

The year is 2222. It has been years since Tears of the New Moon, a mysterious rain, poured and wiped out almost the entire human race. The poisonous rain gave birth to deformed creatures devouring humans, and humanity fled from the danger. As means for survival, the humans then build an underground haven; Amasia. In this newly built dystopian city, in a pursuit of maintaining their existence, they run into an Artificial Intelligence named Magus. Not knowing how things will work between them, the story of how Humans and AI coinciding and trying to find their truths begin.