Arin is a human world classified as a "Core Planet", meaning it is a great center of political influence, economic development, and military strength that is of critical or strategic importance for humans. As a core planet, Arin provided significant financial, material, and other resources to AE and the Knight Order while being exempted from mandatory conscription although its self-defense group, AUA, still voluntarily deploys expeditions to the frontiers. Arin is different from all other core planets in that it is de facto seen as the capital of humanity due to being the host planet of the Central Order Headquarters of the Knights. Given its power and wealth, it is presumed that the scope of Arin is very broad. Besides Planet Arin, Arin also encompasses several nearby colonies orbiting the planet such as the 7th Colony of Arin and other bodies within the same system.
Both the Main and Another episodes of Knight Run are either set in Arin or are highly influenced by the events that came from it. As such Arin is a central setting to the whole series. Main Episode-0 Pray covers the Pray War which saw the fall of Arin and the struggle to retake it from the Beasts.
First Battle of ArinEdit
- Main article: Pray War
Arin maintains a highly disciplined, experienced, and modern self-defense force known as the AUA. It is an extremely distinguished and reputable military force due to having a very powerful potency despite being a self-defense force only. It is implied therefore that AUA is the largest armed force there is, second only to the main unified force of the AE alliance.
The AUA is very active in participating in the Human-Beast conflict. It routinely sends expedition forces to the frontiers to provide auxiliary reinforcements to conflict zones and other battles against Beasts.
The Knights settled in Arin when they restructured themselves from the humanitarian aid support/anti-Beast R&D organization "PF" to the independent paramilitary group known as "Knight Order". Eventually, the Knight Order decided to expand their structure upon gaining official recognition and support from AE. The Northern, Eastern, Western, and Southern Orders were established as branches of the main Central Order that remained in Arin as the overall supreme command and headquarters of the Knights.
The Knight Order subsidiary, Knights Training Organization, was staffed and handled by Central Order. This made Arin the main recruitment and evaluation site for prospective Knight trainees.