We know that the first episode has a lot of details that's why when I was rewatching it, my eye caught the design of Father Katri's shawl: the right side has the symbol of the moon and darkness, and the left side has the symbol of the sun and light.

Sophia's dialogue in the first episode, where she said "the light shines in the darkness," or when the sun rose and she told Elgin, "The sun has returned!"

Even when Henry drank the man in yellow,s  blood, all the walls were painted yellow, and there was a wall clock with a sun design on it. There was even the color purple, which in color theory is the contrast to yellow, and Sophia mentioned it's not her favorite color.

Now we've seen that at the end of the cycle, the phenomenon of the sun and moon got disrupted, and everything was destroyed altogether. We also saw the man in yellow playing with the boy in white  and in that place, there is something ancient.

I think the relationship between the man in Yellow and boy in white is a father-son relationship. We know that children are born in darkness and sacrificed in darkness meaning each time, the moon and darkness are attributed as symbols to the children, and the sun as a symbol to the villainous character, meaning the man in yellow .

Even the opening theme of the series is about a father and son but this father and son are something ancient, meaning God and Satan.

MIY and BIW