Arthur and Shinra are both third-generation pyrokinetics working as Fire Soldiers of Company 8. Although it hasn't been touched in the story, Shinra and Arthur already met prior to being assigned to Company 8 in the Academy, but is unknown how long they've known each other. Shinra apparently knows Arthur well enough to accurately interpret his sounds, like "hmph" which to others would sound like he's acting cocky or stubborn; but to Shinra it's just Arthur being "too stupid to come up with anything to say."
A common argument they would have is whether knights or heroes were better, with Arthur on the side of the knights and Shinra on the side of the heroes. After Shinra told him that "knights were wussier than heroes" Arthur started declaring himself the "knight king" instead of just knight. He seems to forget to add 'king' at the end sometimes and has to tack it on last second; which annoys Shinra to no end.
Arthur accompanies Shinra to "save a dog" that was supposedly stuck in a tree, said dog ended being Mamoru. After getting the mascot down, they help out with handing out balloons. After the alarm is called of the appearance of an Infernal, Arthur hops on Shinra's back so that they could get to the Infernal quicker. They work together to fight off Setsuo, but Arthur is ultimately left behind after Setsuo flees and Shinra follows him.
Although the two have their disagreements and often bicker, Arthur does have some amount of concern and cares for Shinra. After Shinra starts acting weird and feels better after cooking dinner and talking with Takehisa; Arthur gives Shinra more food from his plate since Shinra's appetite improved along with his mood.
In Episode 13, Arthur deflects a fire arrow from the White Clad that was fired at Shinra. They fight together and is shown to have exceptional teamwork and sync.
- In the opening they can be seen holding hands while falling towards an Infernal.
- Having an eating contest at Ippudo Ramen, then getting scolded by Obi for eating too quick.
- Sneaking into Karim's room; Shinra gets angry at Arthur for damaging the lock.
They are the current most popular ship in the Fire Force fandom and growing as the story progresses.
Arthur finds Shinra's nervous smile cute, even though he constantly makes fun of Shinra for it. Many fanworks depict them as good friends who bicker in public but a lot more friendly behind doors or alone.
Because the two canonically share a room, some fanworks revolve around the two sharing a bed.
- Shinra was jealous of Arthur's popularity with the girls in the Academy.