The world was narrow, and it was cold... at least, that was how it had always felt to them.
For the twin demons Cento and Cien, the era into which they were born was a difficult one to navigate. Unlike humankind, demons did not always have parents. This was especially true for those known as Unique Species, who often manifested directly from magic power. For such beings, it was rare to have siblings, let alone a mother or father.
Because they were twins, their world had become a closed circle, encompassing only the two of them. It was a dark, frigid existence that lacked any sense of external warmth.
At the time of their birth, the Demon Realm was on the cusp of a great transformation. The systems of the Six Kings and Peerage-classes were beginning to take root, and the social order was shifting. The sisters survived this era of upheaval by leaning on one another, working as handymen out of a large city.
Fortunately, the chaos of the transition meant that there was plenty of work for those willing to do it. Earning enough money to keep themselves fed was never particularly difficult.
Cento and Cien were perfectly content with their lot in life. They possessed significant combat power; had they wished, they could have easily joined one of the major camps and attained a respectable rank.
Yet they never felt the urge. As long as they had each other, they were satisfied. Having spent their entire lives in their own private world, they had no desire to serve a master or form deep connections with others. They remained independent, moving through the city as shadows, touching the lives of others only as much as their work required.
Then came the turning point. It happened with a suddenness that caught them both off guard. They had spotted a demon in town who looked lost and decided to offer directions. It wasn't an act of charity; they simply assumed they could squeeze a bit of pocket change out of the encounter.
"Really!? That's a huge help!"
The woman had purple hair and a vibrant energy. They guided her to her destination, collected their small reward, and thought nothing more of it—until they found her lost in the exact same spot the following day.
They stared at her in exasperation, wondering how someone could fail to learn a route after being shown it once. The woman noticed them, beamed, and asked for their help again.
When they found her in the same place for the third day in a row, they couldn't help but sigh.
"...Alright, why have you been lost for three days straight in almost the exact same spot? Are you an idiot?"
"It’s the strangest thing," the woman replied. "The scenery looks completely different than it did yesterday."
"That's because you're one street over..."
Cento and Cien were truly appalled. The woman—who introduced herself as Tre—merely gave a sheepish, wry smile.
"Ahaha, sorry. To be honest, I'm on a long vacation for some sightseeing, but the streets in this city are so complex!"
"No, usually after the first time... or the second at the latest, a person would take some kind of countermeasure," Cento pointed out as they led her along for the third time.
Tre just waved a hand dismissively. "It's fine! In this world, most things have a way of working out!"
"...No, they clearly aren't working out, which is why you're lost right now," Cien retorted.
Tre laughed brightly, as if she didn't have a care in the world. "But they are working out! After all, you two found me again, didn't you?"
"...We only did it for the reward."
"Oh! I know! If that's the case, why don't you just act as my guides for the rest of my vacation?"
"Cento..."
"...I see. You want us to be your personal tour guides for the duration of your trip? That will depend entirely on the reward."
"Hmm, let's see... what sounds fair?"
The twins had already concluded that Tre was an airhead. Cento figured they might as well accept it as a formal contract; it would be an easy job, and Tre didn't look like someone clever enough to pull a scam.
"It's a thirty-day trip, so how about three Gold Coins?"
"..." "..."
The twins froze. They asked Tre to wait for a moment and retreated to a secluded corner to deliberate.
"Three Gold Coins for thirty days of guiding? Cien, what do you think?"
"It’s incredibly suspicious, but she doesn't seem like she's lying. Maybe she's the daughter of some wealthy noble?"
"A sheltered girl with deep pockets... that fits the profile. But why would someone like that hire two kids like us? We're basically vagrants."
"Should we take the risk? We'll stay on our guard, of course."
"With three Gold Coins... we could finally buy a Magic Tool. Let's do it."
At the time, Magic Tools—many of them invented by one of the Six Kings—were just beginning to become popular. They were incredibly convenient but far too expensive for the twins to afford. They weren't looking for luxury, but they desperately wanted a Magic Box so they could store food without it spoiling.
Seeing this as their chance, they accepted Tre's request.
What followed were thirty days of being completely at Tre's mercy. Her relentless optimism and her "it’ll work out" attitude made even the simplest tasks an ordeal. Tre insisted that Cento and Cien join her in every activity, treating the sightseeing as a group outing rather than a professional service. Since she was paying for everything, they had no reason to refuse, but her sheer energy was exhausting.
Tre was a force of nature. She was a master of enjoyment, her eyes sparkling with wonder at every new sight, reacting to the smallest things with infectious joy. To the twins, who had lived such a muted, isolated existence, Tre’s presence was blindingly bright.
Being dragged around by her led them to discover things about their own city they had never known. They ate at high-end restaurants they would have never dared enter and were stunned by the quality of the food. With each passing day, their conversations grew longer and more natural. The feeling of "doing a job" gradually shifted into "enjoying a trip together."
As the thirtieth day approached, an unfamiliar loneliness began to take hold of their hearts.
Their world had been a circle of two. But a third person had forced her way inside. In a world they had always found cold, they had discovered a warmth they could no longer ignore.
"...Hey, why don't you two come with me?"
When the contract ended and Tre made her offer, it shook them to their core. Her smile was too dazzling to turn away from, and the hand she reached out to them was far too warm to let go.
The twins took that hand. Tre led them to Kuromueina and her family, and from that point on, their world only grew wider and warmer. Under the Underworld King’s guidance, they gained immense power. Eventually, they volunteered to serve as Tre's guards—a way to repay the woman who had reached into their dark corner and pulled them into the light.
In the present, Tre lay sprawled across her bed with a look of pure exhaustion.
"...That was brutal. Do they really have to scold me for that long?"
Cento and Cien exchanged wry smiles. Tre had just been thoroughly lectured by Ein and Zwei. Even though she looked defeated now, they knew her well enough to know she’d be back to her usual carefree self in no time.
This, of course, was precisely why she was constantly being lectured—though neither of them believed she would ever truly learn her lesson.
"...Tre-anesama, would you like something to drink?" Cento asked.
"Oh, Black Tea would be great! The one we got the other day with the orange scent!"
She was already bouncing back. The twins sighed, knowing it was only a matter of time before she forgot this ordeal and wandered off on another unauthorized adventure. It was a headache, to be sure, but they adored her far too much to ever truly lose patience.
"By the way, listen to this! I went to a seafood place Kuro-sama recommended, and it was amazing. We have to go, just the three of us, next time."
"Ah, I know the place. Cien and I were curious about it," Cento replied, beginning to brew the tea.
"What did you have, Tre-anesama?" Cien asked, bringing over some sweets and sitting at the table.
Once, the world had been narrow and cold. Once, their world had been a circle of two. But that was before they met the sun—the girl who bore the name of "Three," whose light had changed their world forever.
Tre A woman with an indomitable, positive spirit, though her actual combat power is quite fragile. She is a boundless mood maker and is deeply cherished by her family. She believes everything in life will work itself out, which means she is almost always smiling... and almost never learns from her mistakes.
Cento & Cien Twin demons who have a unique history within Kuro's family; they were not found by Kuro herself, but were brought home by Tre. Although they are constantly exasperated by Tre's antics, they both absolutely adore their "older sister" and frequently spoil her.
Tre's Bracelet A Magic Tool similar to Kaito's necklace. Kuro imbued it with various magic formulas to protect Tre; if she is ever in genuine danger, Kuro will be alerted immediately. In fact, the necklace Kuro gave Kaito was a prototype created while she was designing Tre's new bracelet. She had used the necklace format to test the balance of the automatic activation and the complexity of the magic formulas. (Since then, Kaito’s necklace has been customized specifically for him, so the internal formulas of his necklace and Tre's bracelet have diverged significantly.)