Koumyou Sanzo:

Koumyou is inherently holy, and is the moon (and thus the moonlight).

On top of that, he's wearing the concept of light and holiness and restoration itself, the Seiten Sutra, around his shoulders. As a reminder because it's been a while, this is the info I had on my app about it:

Long ago, Shakyamuni Tathagata spread forth a sutra across the heavens, from which was born existence and void, light and dark. The earth was created thence, where life and death came to be. Shakyamuni tore apart the sutra into five pieces and entrusted its fate into the hands of the people Below.

Seiten Scripture: One of the Founding Scriptures of Heaven and Earth. It manages “holy” or “yang”, and falls under restoration. Unique to the Seiten Sutra, it has healing and restorative powers. It has the power to create light.

All five of the sutras are indestructible, and have a form that drapes over the shoulders of their Sanzo, and a form where it's a scroll. Upon activation, a potentially limitless number of tendrils of the scroll move through the air, guided by the Sanzo it's attached to, and can be used offensively or defensively as the Sanzo sees fit.

There is something of a blurred line between a sutra and its Sanzo, Koumyou himself actually has some of these properties since it's bound to his soul.

...Sooooo, all that is to say... I think it's safe to say Koumyou will be highly effective against the demons, and highly resistant to the demon realm's dark/death/decay bullshit?

Yes?

Possibly even able to shield others near him from that shit, with the sutra, if needed?