Arthur's Adventure arc

The Arthur's Adventure arc is the eighteenth story arc of the Fire Force manga series.

Arthur is left dejected after his defeat and the destruction of Excalibur at the hands of Dragon. Vulcan attempts to cheer him up and ready him for future battles by creating an elaborate adventure to create a better sword.

Summary
A sulking Arthur is visited by Vulcan after he recovers from his injuries. When Vulcan offers to fix Excalibur Arthur tells him that the blade was special and cannot simply be repaired with normal metals, unlike the one's used at the hardware store he brought Excalibur from. Vulcan offers to take Arthur on a quest to find Orichalcum to forge a true holy sword much to the Knight King's delight.

In reality, Orichalcum is a myth and Vulcan is using this as an opportunity to reinforce Arthur's self image in order to increase his power. He, Lisa and Yū join together with local townspeople to create a fake quest so that he can have Arthur discover the steel Vulcan plans on using. Unfortunately, Arthur's delusions and intelligence lead him to overthink the riddles meant to lead him back to the starting point. So while Benimaru and Joker discuss possible allies in the fight against the Empire, Arthur decides that his quest must lead into the Netherworld and he drags the trio down with him thinking that going down will lead him to the start of civilisation, Atlantis. Despite Lisa's history of the Nether causing her grief and Yū's total fear of the underworld, the four march on. After an hour of aimless wandering Lisa tries to create a fake monster with her powers to get Arthur to go home but he sees through it quickly and accuses her of not taking things seriously. Suddenly Arthur senses something coming from the darkness and he comes face to face with his lost parents, who have been living in the Nether to escape their debts and responsibilities since abandoning him.

His parents praise him for following in the footsteps and seeking to save the world, much to the confusion of all others present. When asked by Vulcan, Mr. Boyle claim they have been the resistance battling the nation's corruption while Mrs. Boyle is quick to admit they are escaping their money problems and she is just indulging her husband's wild imagination. Despite this and admitting that they abandoned their son, the couple have a full understanding of the Evangelist's actions, the corruption within the government, the nature of doppelgängers and Infernals. Arthur's father claims that he is a prophet, able to see the truth and future if he runs away from reality, while his wife thinks her husband just comes up with interesing stories.

Following them back to their hideout full of lost technology, Yū is very distressed to learn that Arthur now has 3 younger siblings and that means his family abandoned him and replaced him. Arthur ignores this while Vulcan finds the fairing of a spaceship and plans on using this to make a new sword due to it's heat resistance.

Returning to the surface, Vulcan uses Aksuka's forge to a new blade for Arthur. After completeing his work Vulcan relaxes and talks to Captain Ōbi about the future and Hibana's recent discoveries. With Vulcan fearing that he won't be able to do anything once the figthing starts, Vulcan gets back to work so that Arthur can be stronger than ever. With a new sword, Arthur promises that he will never be defeated again. Vulcan hands him a 'Stellar Ring' to only be worn when the time is right. Afterwards, Arthur finds another note from his father telling him that the family enjoyed their brief trip to the surface but have left for another 'adventure' without him. While Maki wonders if Arthur is upset, he narrates that he, the knight king twice abandoned and armed with a holy blade, will save the world.