Nodens is a Celtic healing deity, and the son of Belanos, the Sun God, and Anu, his wife. He had a large shrine at Lydney (Lludd's Island) in Gloucestershire, where offerings were made in small bronze models of diseased limbs. He was sometimes identified with the protective Mars or the regenerative Silvanus and his companion and symbol was the dog: a deerhound whose lick could cure the afflicted.
He could have had a following in London, since Lludd's town was supposedly named after him. Nodens is also the name of one the Elder Gods in the Cthulhu Mythos, based on the Celtic mythological figure.
Nodens is one of the various Persona of the Rod Arcana, appearing as the Cthulhu Mythos Nodens instead of the classical Celtic figure.
In Tatsuya's Scenario he resides in the Tower of Memory that is part of the Kadath Mandala. He is an avatar of Philemon and speaks of memories: Of how they are valuable to distinguish one's self, how their memories form together to shape Kadath Mandala, how they influence future generations, and even though the root of the world seems to be ruled by fear and anxiety, but the essence of life is joy. Life will not cease to seek its purpose in a universe heading towards chaos. A life of happiness brings balance while prolonging the life of the world, staving off the heat death of the universe. He then gives them the Trapezohedron of Memory.