Even though he had the "stand-in" effect from the Water of Origin, Kay wasn't one-hundred percent sure things would work out. After all, nobody knew the exact mechanics of how the Holy Grail of Life claimed its price. Celtic magic was weird, totally different from any spells Kay had encountered before—they weren't even playing in the same ballpark. If the Holy Grail of Life managed to bypass the Water of Origin, Kay would genuinely be a goner.
But where things stood now, Kay didn't really have any other choice. He just had to roll the dice!
Naturally, Kay didn't mention any of this to Merlin. There was no point in stressing the kid out.
Kay quickly prepared to use the Holy Grail.
The method for using the Grail was all written in the scroll and wasn't difficult. As long as you knew the technique, it wasn't hard to pull off, and Kay could use it even without knowing Celtic magic.
"tidernas!"
As Kay uttered the incantation, the sky suddenly darkened. The Grail in his hands then pulsed with a gentle, pale gold light. A light drizzle began to fall, and within the rain and the glow, a clear, shining liquid slowly gathered inside the golden cup.
But as the water in the Grail increased, Kay noticed that his own life force was rapidly draining away, like something was sucking it out. Even worse, Kay was completely powerless to stop the process.
As the Grail grew closer to full, Kay realized it wasn't just his life force—it felt like his very soul was being pulled out!
The Water of Origin, which Kay had been counting on so heavily, was completely unresponsive, like a cheap knockoff.
This is it. I'm seriously done for.
That was the only thought in Kay's mind.
Just as Kay was sinking into despair, a sudden, sharp pain coming from the depths of his soul almost made him pass out.
Merlin, who was standing nearby, jumped when he heard Kay's scream. He saw Kay suddenly collapse, clutching his head and wailing. The Holy Grail, as if agitated by something, flared up, shining ten times brighter than before!
Merlin tried to pull Kay away, but an invisible force repelled him before he could get close to the Grail. He was sent flying, hitting one of the Stonehenge pillars and passing out instantly.
So, Kay was left alone to endure the soul-ripping agony.
He didn't know how long passed, but the deep-seated pain slowly faded, and Kay's consciousness gradually returned. When he finally looked up at the Grail again, the cup floating in the air had completely transformed. The golden body was now etched with strange carvings and patterns, and wisps of blue-green flame flickered around it. These flames didn't feel hot; instead, they gave off a strangely warm sensation.
Kay looked at the completely changed Holy Grail, then opened his palm—the Water of Origin was still resting there, untouched.
Kay gave a wry smile.
"Heh, I guess you could call this a blessing in disguise?"
Looking at the system panel in his mind, the energy points he had gained from defeating the Death Knight had vanished at some point. Even the energy bar, which had climbed back up to one-sixth full, was completely reset.
But in exchange, the Holy Grail of Life now belonged to Kay. In every sense of the word!
After thinking it over for a long time, Kay came up with a guess: the Grail's exchange condition was "a life for a life." To save Arthur, someone had to be sacrificed. Kay chose himself, originally planning to use the Water of Origin to survive the cost. However, he realized that the Grail wasn't actually exchanging a life, but a soul!
That's why the Water of Origin was useless. Kay had willingly offered his soul, which was similar to suicide. The Water of Origin wouldn't interfere with a willing sacrifice, which, while totally cold, was logically sound.
Kay genuinely should have died right then and there, but who knows what would've happened if he didn't have the System? His System might be basic, but at least it existed. And since the Holy Grail demanded a soul, and Kay's System was designed specifically to collect souls, the System took the initiative to protect its host by trading its own 'experience' as the price to the Grail.
This Holy Grail, perhaps sensing that the quality of the soul energy Kay provided was exceptionally high, started greedily sucking up more than it should. By the end, it clearly went over the agreed-upon share. So, based on the principle of fairness, it essentially traded a part of itself as 'compensation' back to Kay.
That's why the Holy Grail now completely and totally belonged to Kay.
That was Kay's best guess. Even though there wasn't solid proof, it was the most reasonable explanation.
When Merlin woke up again, it was already night. He was tied to a horse. His first thought was that he'd been kidnapped. But then he spotted Kay, who was riding another horse up front, leading the way. They had left the dead, silent forest and were heading back.
Merlin struggled a bit, realizing that Kay's knot-tying skills were solid; he couldn't break free.
"You're awake?" Kay noticed him stirring before Merlin could even call out. "How are you feeling?"
Kay asked about Merlin while simultaneously untying him from the horse.
"I'm okay... just a bit of a headache," Merlin said weakly as he climbed off the horse, nearly stumbling the moment his feet hit the ground. "And my whole body is numb."
"My bad. I didn't want you to fall off, so I tied the rope a little tight. Just move around a bit, and you'll be fine," Kay apologized without much sincerity, then handed Merlin a canteen of water.
This poor kid was really fragile. He just hit his head and was knocked out for an entire day! If Kay hadn't had some basic medical sense, the kid would have been in serious trouble. It was normal to be weak after not eating or drinking for a day.
Merlin was definitely thirsty. He took the canteen and chugged the water down until he was full. Feeling much better, he finally had the presence of mind to ask about Kay.
"Are you alright? I saw you in so much pain, and I tried to help, but... I don't know what happened, I just passed out."
...
"Seriously, when we get back, eat more steak or something," Kay said to the weak kid. What else could he say? He just patted Merlin on the shoulder as a sign of encouragement.
At first, Merlin didn't quite get the connection and just mumbled, "Oh." But then his face instantly flushed. He's totally looking down on me, isn't he? Absolutely!
But after thinking about it, Merlin realized he couldn't really argue. He was weak. Him saving people? In the end, someone else had to save him...
Merlin's expression shifted constantly as his inner thoughts churned, and he finally lowered his head in shame.
"Alright, everything's fine now. My initial plan was right; the Water of Origin worked after all. What we need to do now is hurry back and heal Arthur." Kay comforted Merlin a bit, then started building a fire to cook a meal.
He wanted to keep going, but he was afraid Merlin wouldn't be able to handle it, so he had to eat and rest before they continued their journey.