After hearing the realm spirit's confirmation, Leon continued to watch Aria and Darlene through the realm spirit's omniscience.
A few moments later, he furrowed his brows and wondered, 'Why are they still collecting the monster cores despite having no use for it?'
'There's actually a use for the monster cores, Master,' Tak-si stated.
'Despite the artificial spirit energy possessing extreme side effects after prolonged exposure to it, all the demons that ever came to this sub-realm had always collected the monster cores for cultivation without exception.'
'However, it's not just demons; many people are willing to ignore the defects for the power they can obtain from the monster cores. Thus, the monster cores can be used as a form of currency, Master,' Tak-si explained.
'I see…' Leon rubbed his chin thoughtfully.
Although he became rich after obtaining a lot of starcore iron, he could only use this form of currency in the Celestial Alliance, where capable artificers could refine the starcore iron.
He couldn't use starcore iron as currency on Gaia.
The monster cores might just come in handy when he explores the demon's territory, and of course, the Geyser Kingdom.
As the only kingdom in the Human Domain with access to the Boundless Sea, he did not doubt that the Geyser Kingdom was possibly using the monster cores as a form of currency as well.
'Hm?' Leon suddenly thought of something serious.
If the Geyser Kingdom relied on the monster cores procured from the sea monsters in the Boundless Sea for cultivation, they would have amassed quite a considerable number of Transcendents—Transcendents that only enjoy half the lifespans.
However, that wasn't the critical point.
The Cataclysm's solar wave had swept the world and brought Wrathful Demonic Energy to every corner of it.
If the Geyser Kingdom did not set up any means of shielding itself from Wrathful Demon Energy like the billowing dark clouds that covered the Dark Abyss Continent, their Awakeners would have rapidly mutated and caused chaos.
'Considering there wasn't any big news from the Geyser Kingdom's borders after the Cataclysm arrived, I'll just assume the Geyser Kingdom had some countermeasures in place…' Leon mused.
It was one big headache he didn't want to think too much about.
It was very likely that the Geyser Kingdom had deeper knowledge and heritage on the Nova civilization, so they should have known what they were getting themselves into.
As long as their problem doesn't spread to the Crawford Empire, he wouldn't care too much about them for the time being.
'Hm? I thought I was the last one to finish my secluded cultivation, but it seems like Duna hasn't exited her retreat yet…'
Leon thought after he shifted his attention to Duna's cultivation chamber.
He recalled Duna mentioning that she wouldn't stop until she completely absorbed the soul energy in the crystallized soul core once she started, but he didn't expect she would take this long.
'…She wouldn't become a Demon King-level existence after absorbing all the soul energy in the crystallized soul core, would she?'
Leon wondered with a startled look.
If Duna could reach the level of Demon King with just the Demon King-level crystallized soul core, it made perfect sense why she treated him like a fool for gifting such a priceless treasure to her.
But given the same choices again, he still wouldn't change his mind.
Nevertheless, was it really possible for Duna to raise her Transcendent-level soul to the Demon King level like that, even if it's a Demon King-level crystallized soul core?
'Come to think of it; I don't really know much about the classification of strength for demons beyond Arch Demon…'
'Tak-si, what is the demon's cultivation ranks after Arch Demon?' Leon inquired shortly after.
'Above Arch Demon is the Celestial Realm for demons, Master. From the lowest to the highest rank, it is Demon Lord, Great Demon Lord, Demon King, Demon Emperor, and finally Demon Overlord.'
Tak-si informed him.
'Great Demon Lord? There was such a level exists between Demon Lord and Demon King? Why haven't I heard about any Great Demon Lord-level tomb in this sub-realm?'
Leon furrowed his brows with doubt.
'That is because the demons regard Demon Lord and Great Demon Lord as one large realm since they don't have any bottlenecks in between. However, the Celestials divided it into two realms to match the Celestial Realm's cultivation ranks,' Tak-si explained.
'I see… That means some of the Demon Lord-level tombs in this sub-realm are actually Great Demon Lord-level tombs…'
Leon thought before he suddenly paused.
The Shadow Tempest Demon Lord had 50 Arch Demon-level Dark Wyrms guarding its tomb.
Leon felt that the trial difficulty posed by Shadow Tempest Demon Lord's tomb was even higher than the Abyssal Wood Demon King's tomb—at least, he felt that was the case for other people that try to challenge them.
'What level was the Shadow Tempest Demon Lord?' Leon asked curiously.
'The Shadow Tempest Demon Lord was a Peak-rank Great Demon Lord, just a step short from being a Demon King, Master,' Tak-si answered.
'I see…' Leon nodded.
It was just as he suspected; the Shadow Tempest Demon Lord's tomb seemed too difficult compared to other Demon Lord-level tombs.
It was actually the tomb of a Peak-rank Great Demon Lord.
'Well, enough of that. What is a Demon Overlord? How is that compared to a Celestial Conqueror? I thought Demon Emperor was the highest realm before True Divinity for the demons?'
Leon raised further doubts.
'Demon Emperor is indeed the highest realm before True Divinity for demons, but the same can be said about Celestial Emperor for Celestials.'
'Hm? What about Celestial Conqueror?' Leon raised an eyebrow.
'Celestial Conqueror is not a realm, but more of a title, given to Celestial Emperors after they successfully bind with the quintessence of star realms or star clusters. They possess the strongest power available to Celestial Emperors, Master.'
'We can also say that they are the Celestial Emperor among Celestial Emperors,' Tak-si explained.
'I see…' Leon rubbed his chin with understanding before saying, 'Then Demon Overlord is just a title given to the strongest Demon Emperor, right?'