The church of the sun was very well known throughout the world of Game, and their branch was present nearly in every capital in the world. They were extremely highly ranked, and their followers believed in the religion deeply.
The main reason for that was that once you joined the church, you would grow in strength very quickly and get relics that the church gave away to the most powerful and promising subjects. But as Kyle has learned, the power was given in the form of pure demonic energy that the church masked as pure qi.
And the relics themselves were the remnants of either those killed or demons that they fought in the demonic realm.
This information of course was secret, and only the selected group of believers of the church knew about their relationship with the underworld.