Axel (アクセル) is a town in Belzerg where occupants are mostly beginner adventurers, and it is where most of the story takes place. It is known as one of the most peaceful, albeit strange, locations in all of the kingdom. The only reason why Axel is somewhat peaceful is because of the presence of both the lich Wiz and the devil Vanir, both former generals who served under the Demon King. Monsters avoid the former, while the Demon Lord's lesser subordinates do so out of respect for the latter. Everywhere else is constantly at the mercy of demon raids and monster sieges. The city does not suffer from starvation or food shortages because it lies on a major migration route, has an early warning system in terms of when crops will attack, and benefits from the large standing army of adventurers to “harvest” said crops.
The town is considered extremely important to both Belzerg and the Demon King's army. Other than the various Japanese reincarnated into the Fantasy World by Aqua, every famous adventurer worth their salt such as Wiz, Brad, and Rosary can trace their origins back to it. Its importance lies mainly because of where it is situated. Surrounding the city are great amounts of beginner-friendly mobs that make for easy leveling for adventurers, such as the giant toads and goblins. People will grind up to a decent level off of these monsters, and then move on to other locations such as the front lines of the war.
After Kazuma brought Aqua with him to the Fantasy World, despite the promise of more Japanese incoming, no more were sent; as a result, Axel was the only location in which rookie adventurers could train up. Due to this fact (and because the Demon King took no more Japanese showing up as a sign that Kazuma was the "chose one"), the Demon King's daughter, the strongest general, took it upon herself to formulate a plan (after Beldia failed) that would wipe out Axel: have Serena infiltrate and put the adventurers under her control using Regina's authority, and then come in and raze the town to the ground. The hope was that, upon hearing the news that no more potential reinforcements would be coming, the front lines of Belzerg's army would lose a great amount of morale and be crushed. Ultimately, however, this plan was foiled by Kazuma, and Serena was sent packing.