"A god-slaying tool capable of destroying gods and Demon Lords?"
In the underground training room, which was gradually turning into a world of ice and snow, Yukinoshita Yukino stared blankly at the (alien/monstrosity) standing behind her, her head feeling completely muddled.
She couldn't comprehend how terrifying this god-slaying tool was, but seeing the spacious basement, large enough to fit several football fields, instantly transform into an ice plain, she finally understood why the Fallen Angel faction considered her a dangerous individual.
Such power, if unleashed in the human world, would cause unimaginable consequences.
The moment she realized this, Yukinoshita Yukino finally felt a surge of fear.
"If such power had appeared on the first day of school, then Mother and Sister..."
They would surely have been frozen solid, just like the tires of that car, right?
And everyone on that street would have turned into ice sculptures, losing their lives.
Just imagine, if someone next to you possessed such power, was completely unaware of it, and could lose control at any moment, wouldn't you consider them a dangerous individual?
And while it wouldn't go as far as wishing them dead, if Yukinoshita Yukino were honest with herself, she would certainly wish for such a dangerous existence to stay far away from her, preferably never to return.
"Do you understand now?" Leo patted Yukinoshita Yukino's shoulder and said, "Such power, if left unchecked, is something no one would want to see."
"So, even if you don't want to become a Demon, you would still be taken away by the Angels or Fallen Angels, unable to return to your peaceful daily life."
"To some extent, many people should breathe a sigh of relief that I've taken you as a Retainer, because it means someone can watch over you, control you, and the risk of you losing control in the future will be minimized."
"How about it? Do you still have any complaints?"
Hearing this, Yukinoshita Yukino was silent for a moment, then sighed.
"I am a bit unwilling, but that doesn't mean I have complaints," Yukinoshita Yukino finally spoke her mind, saying, "I know that in that situation, if you hadn't reincarnated me as a Demon, I would have surely died."
"So, I have never resented you; in fact, I feel some gratitude towards you."
"I'm just not used to it, suddenly encountering such a world and becoming a non-human existence..."
Otherwise, with Yukinoshita Yukino's personality, how could she obediently follow Leo around?
While she wasn't very keen on becoming a Demon, the fact that Leo saved her was undeniable, and the fact that she survived because of him was also undeniable. So, Yukinoshita Yukino had already accepted this outcome; she just wasn't quite used to it and still harbored some unwillingness.
Now, truly realizing how terrifying her power was, Yukinoshita Yukino had also adjusted her mindset.
"Setting aside other matters for now, can you first teach me how to use this power?" Yukinoshita Yukino turned to Leo and said with extreme seriousness, "I don't want this power to appear uncontrollably anymore."
"Don't worry, that's what I'm going to do next," Leo said readily, "Whether it's the power of a Demon or the power of a Sacred Gear, I will teach you how to use them."
She was his first Retainer, and a potential stock with infinite possibilities; not properly training her would be a terrible waste.
He still had many things to do in the future, whether it was restoring the Erigor Family or debuting as a new pure-blooded High-Class Devil, he would need powerful Retainers to help him and allow him to go further.
Not just Yukinoshita Yukino, he also needed to work hard.
After all, he was also a god-slaying tool Wielder, and the second-ranked superior god-slaying tool... After deciding what to do next, Leo didn't immediately begin teaching but first took Yukinoshita Yukino to the fourth floor of the manor, to a study.
Here, dozens of bookshelves were densely packed with books, none of which were from the mundane world, but rather books related to the mysterious.
These were once the collection of the Erigor Family; after Leo inherited the Erigor surname, these books were gradually sent back to him by the Underworld, including some particularly precious family ancient texts.
Over the years, Leo had slowly learned about Demon knowledge from these books, which also contained the secret arts passed down through generations of the Erigor Family, the most suitable magic power training methods, magic power application methods, specialized detection ability usage methods, and precious ancient magic books passed down by the Erigor Family's ancestors, all of which were invaluable.
Unfortunately, due to the past rupture, many of the Erigor Family's treasures were lost. The ones before them had also been seen by various Demon families in the Underworld, and were no longer as precious as they once were. However, for Leo and Yukinoshita Yukino, who needed this knowledge, they were undoubtedly still very valuable. For ordinary beings without a background, their value was not diminished at all; if they were to fall into the outside world, they would definitely be fiercely contended for.
Leo handed Yukinoshita Yukino a book containing magic power training methods, asking her to memorize its contents and first learn to use her own magic power. He, meanwhile, searched the bookshelves for books related to Sacred Gears and began to learn about their use.
Sacred Gears have existed in the world for a long time, and various forces have encountered Sacred Gear Holders over the long years. Their understanding of Sacred Gears, even if not as specialized as that of the Child of God Monitors, was not completely ignorant.
Both Leo and Yukinoshita Yukino needed this knowledge and guidance to slowly learn how to use their own Sacred Gears.
Thus, the two simply took leave from school and stayed in the manor, diligently studying.
This made many people at Sobu High School who had seen the two come to school begin to imagine things.
A boy and a girl both came to school, but then weren't in their classrooms all day and instead took leave?
Who would believe there was nothing fishy going on?
Especially since someone confirmed that Leo and Yukinoshita Yukino entered the Service Club activity room together and hadn't come out since, which made it impossible not to suspect what they were doing in there.
Thanks to this, the rumors about Leo and Yukinoshita Yukino spread smoothly throughout Sobu High School, leading to no small impact later on.
However, these matters were currently irrelevant to Leo and Yukinoshita Yukino, and the two were completely unaware that rumors about them had spread at school, still diligently studying in the manor.
In the evening, Leo still didn't let Yukinoshita Yukino go home.
"You're already my Retainer, so there's no problem with you just living here."
This sentence made Yukinoshita Yukino show a wary expression.
"I feel my chastity might be threatened, so I refuse."
Yukinoshita Yukino said such words without hesitation.
Unexpectedly, Leo raised an eyebrow, his gaze lingered on Yukinoshita Yukino's chest for a moment, then he showed a look of utmost disdain.
He said nothing, yet seemed to have said everything, causing Yukinoshita Yukino to clench her small fists.
"Say what you want to say!"
"No, I don't want to say anything."
"But your ill-intentioned, extremely lewd gaze has already betrayed you."
"Alright, assuming I actually harbor ill intentions."
"Are you trying to defend yourself?"
"I just want to tell you that it's important for people to have self-awareness."
"Are you saying I'm not cute? No one would have bad intentions towards me?"
"Don't say that, there will still be such people. Maybe some people find small things cute too?"
"!!!"
After a brief exchange, Yukinoshita Yukino lost control of her emotions again, causing the pure white ice princess to appear behind her, silently releasing astonishing cold air.
But just as Yukinoshita Yukino felt a sense of dread because of this, Leo casually raised a hand, snapped his fingers, and made the astonishing cold air disappear instantly.
It was only at this moment that Yukinoshita Yukino realized how strong Leo truly was.
In her opinion, the power she released was already terrifying, capable of causing widespread freezing phenomena with ease and possessing astonishing destructive power. Yet, such power was effortlessly dealt with when facing Leo.
"Is this the power of a High-Class Devil?"
Yukinoshita Yukino gained her first real understanding of Leo's strength.
"It's just that you can't use your Sacred Gear very well yet."
Leo replied.
The disappearance of that astonishing cold air wasn't due to the power of a High-Class Devil, but the power of the Blazing Heaven Thunder Prison.
The Blazing Heaven Thunder Prison could freely control weather and natural attributes, and ice attribute power was one of them. And the ice princess was only the eleventh-ranked god-slaying tool, considered lower-tier among god-slaying tools. It was naturally possible for Leo to interfere with her power using the power of a superior god-slaying tool.
Of course, this was also because Yukinoshita Yukino was still too weak at present, unable to properly use her own Sacred Gear or her own magic power, which was why she was suppressed by Leo. Otherwise, if they were both god-slaying tools, even if Leo could control the opponent's power, it wouldn't be so easy.
"Keep working hard."
Leo appropriately admonished his Retainer, making Yukinoshita Yukino show an unwilling expression.
In the end, Yukinoshita Yukino still stayed overnight at Leo's manor.
There was no other way; her apartment couldn't support her training her power like this.
Moreover, Leo also told her something.
"Get ready; the meeting we discussed earlier is about to begin."
The High-Class Devil representing the Underworld in assisting Leo and responsible for liaising with him was about to arrive here... Night fell quietly.
When the sun had completely set and the sky was covered by darkness, Yukinoshita Yukino finally experienced the situation Leo had mentioned during the day.
As soon as night fell, Yukinoshita Yukino immediately felt her body, which had been somewhat sluggish during the day, suddenly start to operate smoothly like a wound-up machine.
Power began to surge within her, and her spirit became excited, as if a fish had returned to water. The night, which normally instilled instinctive fear in humans, made Yukinoshita Yukino feel extremely close, and she even seemed to possess night vision, allowing her to see far into the distance even without light.
Under these circumstances, the two went down to the basement together.
There, the Magic Circle drawn on the ground was becoming increasingly brighter.