Brute forcing it

"Idea about what?"

"Hello, Merling, are you here? What do you mean 'idea about what'? About engraving runes on our bodies!"

"What? How could you ever possibly have an idea about something that even the greatest of experts have been unable to do for almost 100,000 years?"

"Because they are them, and I'm me. The difference is near infinite! Now shut up and listen. What if everyone who has a cultivation talent, has a certain corresponding rune or that the talent itself is a rune? In that case the body is capable of being engraved with runes. Just very specific ones?"

"Do you think no one has ever thought about that? There has been countless research done regarding this exact idea, one even done by me. No matter what rune you use to engrave upon your body, it won't work, whether it coincides with your talent or not"

"Listen! You can't just use any random haphazard rune, you need to use your personal one. All these books say that for everything under the good graces of the Heavens will have a corresponding rune. Well, humans fit into this category. Presumably the rune will be some combination of the human and talent runes. Say you have a fire talent, your corresponding rune will be an evolved form of 'fire' and 'human', becoming something more advanced"

As Samuel continued to explain, the more convinced Merling became.

"So, what you are saying is that since I have two talents, spirit eyes and spirit arrows, my personalized rune will be a combination of them as well as human. That makes a lot of sense. But how are we supposed to know which combination is the correct one"

"When in doubt, just brute force it. Well try every possible comprehensible rune combination we can, engrave them all onto your body, and test if they work"

"Okay, let's do it!"

However Merling shortly came to regret those words. He was too engrossed in the potential of succeeding in this dream of his, that he forgot you had to physically carve the runes into your flesh. You can't use ink either. One needs to prepare their own blood, before adding spiritual qi into it, turning it into a good rune ink, before using a special carving knife dipped in it, to carve and write the rune. To say it would be painful would be an understatement.

"Don't give me that look. You have already said you'll do it. What, you gonna renege on your words? Do you have such little honor?"

Samuel was clearly instigating him, but unable to lose his hard earned face, Merling refused to back down.

"No, I was only pitying you for not getting to be the first person experiencing this breakthrough. Now let's get to it before I decide that you would be better to try this on"

"Such a selfless and honorable character you have, teacher. We should make sure that the rune is connected to the spiritual qi in the air, but doesn't react to it. Also we need to make sure that there is at least a teeny tiny little reaction from you injecting your personalized spiritual qi into it. Only when we can confirm both of these, will we engrave them on you"

Merlin was grateful Samuel was thinking like this, honestly he was so embarrassed he was ready to just start cutting himself bloody left, right and center.

"Let's start", they both said at the same time.