After leaving him to spin in the air like a ceiling fan for a while, Cain let Ren down and watched as he ran off to the bucket.
A few moments later, Ren looked up and shot him a resentful glance.
"You urgh, just saw me eat... How could..."
Ren couldn't finish talking before he continued barfing his guts out.
Cain shrugged.
"Who told you to tackle a Wizard as an Attuned? You brought this upon yourself."
Cain continued watch Ren as he was kneeling over the bucket.
"So, how did you do it, you little overachiever?"
Ren looked at him with worn-out eyes.
"Do... phew do what?"
Cain raised an eyebrow.
"Movements like that should be impossible for an adept with elementary control. To lunge at me like that, you'd need at least intermediate control."
Ren's eyes widened.
"Wait, so... I reached intermediate control? Is that why it felt easier to move my Ether than before?"
"Hold on, did you just say easier than before? So, you just reached intermediate control?"
Ren nodded, and proceeded to recount to Cain the difference between him controlling his Ether this morning and a few minutes ago.
Cain rubbed the light stubble on his chin.
"Hmm..."
The calm contemplating look on his face was incongruent to his inner thoughts.
"Ok, so to sum up, this kid attuned two weeks ago, achieved elementary control in two weeks, and advanced to intermediate control in a day... How exactly am I supposed to report this without sounding crazy?"
Cain let out a heavy sigh.
"My best guess is that the rampage you had earlier enhanced your Ether acceptance."
Ren tilted his head.
"But aren't Ether rampages my Ether going out of control? How would that lead to my control improving?"
Cain shook his head.
"No, you're partially right, but you're missing the whole picture."
He took a deep breath.
"True, an Ether rampage is essentially losing control of your Ether, but have you ever considered what you're actually losing control to?"
Ren's face sank.
"... N-no."
Cain assured him.
"Don't worry, most people just think of it as the price to pay for power, which it is..."
"But that's not the whole story."
His voice deepened.
"When a human attunes to a spirit, that spirit doesn't vanish. Instead, it becomes part of the Attuned's soul, attuning their body to the spirit's element."
Cain's expression visibly shifted.
"But the devil lies in the details, in this case, almost literally."
Ren gulped.
"T-the thing we lose control to... is the spirit."
Cain nodded.
"... Yes, whenever a Striker's emotions become unstable, their Ether reacts to that disorder, which in turn, destabilizes their Ether core, the center of their soul."
Ren felt his heartbeat quicken.
"Wait, then since the spirit is part of an Attuned's soul, if the center of the soul is destabilized..."
Ren's voice grew heavier.
"The spirit gains an opportunity to control the Striker's Ether, to kill him and set itself free!"
Cain shook his head.
"Close, but no. When a Striker's spirit is destabilized, the balance of control shifts to the spirit leaving the Ether in the Striker's body at the disposal of the spirit."
Ren almost interrupted, but he decided against it.
"Until this part, you're basically right, however, when a spirit takes control of a Striker's Ether, it doesn't try to kill him per se, it tries to take over the body from within, by emptying out the body's Ether, and encasing it with the Ether from the outside, facilitating the synthesis between the spirit and the Striker."
At this point, Ren felt his heart in his throat.
"No, wait, surely you can't mean... No way, right?"
Cain nodded somberly.
"Yes, the spirit then takes over the soul and body of the Striker, and not only becomes much smarter, but its strength also essentially doubles, because it becomes a whole new being born from two creatures of the same class."
Cain paused.
"We call those beings... Demoniacs."
Ren sat there in silence, digesting the information he was just told.
A few moments later, he looked Cain in the eye, no visible change in them from before, other than a little surprise.
"I see... but why didn't you tell me about this before? And how does this relate to me achieving intermediate control?"
Cain's lips curled up a little.
"Well, to answer your first question, I didn't tell you before because there are certain things that I am not allowed to share with people outside the Striker corps. In fact, you're in for a treat after you leave this room."
"As for your second question, the process itself in which the Ether tries to escape from the core means that it's forced to travel through your body, and while it's extremely painful due to how violently the Ether moves, it's similar to the method to evolve from Attuned to Marked."
Ren's face lit up with understanding.
"I see! So in the process of escaping, it got my body more used to Ether, which led to my control being enhanced."
Cain nodded.
"Correct, although it's a rare occurrence, and it only happens to Attuned whose bodies have yet to adapt to Ether."
"... I don't know if I should say I was lucky or unlucky."
Cain put his hand on Ren's head.
"Well, lucky or not, what's important is that you're alive, beyond that, you're more than ready to leave the waiting room now."
Ren's eyes lit up.
"Wait, really?! I'm finally leaving this he— ehem, waiting room?"
Cain raised an eyebrow.
"Yes, I was planning to take you out tomorrow morning if you had reached elementary control as I had suspected, but you went beyond that and even achieved intermediate control. Now, it's going to be a little longer and I'll come pick you up around noon."
Ren scratched the back of his head a bit.
"Sorry, I guess?"
Cain just stared at him blankly.
"Just go rest for now, today was a long day, and it's already late. You must be exhausted."
Ren focused on himself for a moment, to assess his current state. All he felt in his body was exhaustion and an overwhelming desire to sleep.
"You... might be right about that."
Ren moved over to the bed and sat on it, feeling himself sink into it.
"Well, I'll go now, just take your time and rest. I'll come pick you up at noon."
Cain left both Ren and his room in rough shape, and thought about the report he'd have to make once more.
Ren lay on his bed and drifted to sleep almost immediately, the mental and physical fatigue of the day falling on him at once.
...
At night, under Ren's covers and shirt, his chest glowed with a faint, white light.