Aru began as a simple shrine to Bishamon, but although only a few monks resided on the site, pilgrims still made the long and difficult journey through the Ikuyu Mountains. Since there were no facilities, they endured the elements during their stay. Eventually, due to the number of pilgrims falling victim to the tough journey, buildings were erected on the site to allow them to stay in greater comfort.
Through a combination of pilgrims setting up permanent residence and people setting up stall to make a profit from providing services to the pilgrims, the settlement began to grow. Over a few decades, a town existed on the site of the shrine, although since it had no daimyo or official government, it was not recognised as such. The monks used their skills to protect the population from surrounding threats such as bandit invasions.
The shrine on the site of the town continued to grow as a result of increased donations from the population and the ever-increasing stream of pilgrims, and became the Shining Temple of Bishamon.