The golden eyes meet the red eye

"Merlin, as the keeper of magic, must control what is happening in Japan, from which he feels that new types of magic are coming.
He learns of Yakumo Saitou, who has the ability to see ghosts, and decides to meet him.
He finds a grumpy boy with a red left eye."

In response to a prompt by Rox08 in the Merthur_prompts collection on Ao3.
Prompt: "After Arthur's death, Merlin travels around the world discovering and seeing how many different types of magic exist and becomes their keeper.
One day he hears about a boy, named Saitou Yakumo, who can see the soul of the deaths.
He goes to investigating.

Or: Merlin meets Yakumo."