Having finished her afternoon consultations, Fia happened to glance toward a metal tin sitting in the corner of the room. It had originally contained tea leaves, and even though the contents were long gone, she still used it as a small storage container.
It wasn’t particularly stylish; it was just a common brand of tea found in any shop. The only reason Fia still kept it was because it was a gift she had received from her family back when this clinic first opened.
This takes us back several centuries.
Fia—one of Kuromueina’s family members who had once called herself the Demon King and invaded the Human Realm—had left her family, vowing to spend her life in atonement for her grave transgressions.
While she had always been talented in recovery magic, she spent her time traveling through the Human Realm to study human medicine. Once she had gained sufficient skill as a physician, she established a clinic in the Kingdom of Sinfonia.
To put it plainly, the members of her family—commonly referred to as the Underworld King Faction—were exceptionally capable. Had they truly wished to track Fia down, they could have done so with ease.
In fact, most of the family was aware that Fia had begun her new life as a doctor in Sinfonia. However, not a single one of them tried to visit her.
They understood Fia’s suffering and regret. They believed that both she and Kuromueina needed time and space to find peace in their own hearts.
However, there is an exception to every rule.
Exactly at the moment Fia had finished building her clinic and was preparing to start her practice the very next day, a visitor arrived.
"Fia! I came to visit~! Oh, and I brought a gift. I found some delicious tea!"
"...Wh-What? Tre? Why are you..."
"I heard you built a clinic, so I came to see it! Think of it as a housewarming gift!"
It was Tre. It went without saying that Fia was bewildered by her sister's sudden appearance. Fia had been keeping her distance from the family due to a whirlwind of emotions, including guilt and agonizing regret for her past actions... but Tre simply wasn't the sort of person to dwell on such things.
Practically forced out of her own doorway, Fia watched as Tre entered the house, brewed the tea she had brought, and began chatting away happily.
Seeing her sister acting no different than usual was a joy, yet Fia’s conscience told her she couldn't allow herself to be indulged like this.
With a serious expression, Fia looked at her sister across the teacups and spoke words intended to indirectly urge her to leave.
"Big Sis Tre, listen. I committed a terrible mistake. I can't face the family right now. I don't have the right to see anyone... No, to be honest, I have no intention of seeing anyone from the family for the time being. Everyone else understands how I feel, which is why they've been considerate enough to stay away."
"I see... By the way, something hilarious happened the other day."
"I thought so! You don't have a lick of restraint, do you, Big Sis Tre?!"
Tre was naturally not the type to listen to reason, and Fia could do nothing but clutch her head in exasperation.
"...Wait, Big Sis Tre? Where are Cento and Sien?"
"We got separated. Isn't that weird?"
"..."
Fia’s gaze grew distant. She couldn't very well cast out her sister, who possessed zero combat ability, so she ended up keeping Tre company until Cento and Sien eventually caught up.
Tre continued to visit the clinic frequently after that. Fia tried to persuade her to stop several times, but by the fourth visit, she gave up entirely.
Tre truly did just come to play. She would pop in out of nowhere, ramble about random topics, and then leave. She never reproached Fia for her past, nor did she try to pressure her into reconciling with the rest of the family or Kuromueina. She was simply there to talk.
Because of that, even Fia couldn't bring herself to reject her harshly.
Tre often appeared thoughtless, but she frequently used her intuition to grasp the heart of a matter. Regarding this situation, she recognized that bridging the gap between Fia and Kuromueina was beyond her... No, she knew it was impossible for me.
To save Fia, one would have to first strongly reject her self-pity and then drag her before Kuromueina by force. Tre knew she lacked the capacity for that.
It wasn't a matter of physical strength. Even if Tre were to condemn Fia, those words wouldn't reach the depths of Fia's heart. Fia would either casually brush them off or offer a shallow apology, and her resolve would remain unshaken.
Only the words of an existence that accomplished what Fia could not—someone Fia absolutely could not ignore—would be able to draw out the true feelings hidden deep within her.
Tre hadn't grasped the logic quite that perfectly, but she vaguely understood that it was a task she couldn't fulfill. Since she was a positive monster by nature, she simply figured everything would work out eventually and continued her visits.
It didn't bring about a sudden revolution, but the sight of her sister's unchanging attitude provided Fia’s heart with a much-needed sense of security.
Eventually, the singularity known as Kaito Miyama mended the relationship between Fia and Kuromueina. Not long after, Fia returned to Kuromueina's castle—her beloved home—in the Demon Realm.
After being punched with all her might by Funf, who loved her like a sister, and then being subjected to a grueling multi-hour lecture from Zwei, Fia was trudging through the halls in a daze. It was then that she happened to run into Tre, who was on her way back in.
"Oh? Fia?"
"T-Tre. Um, you see..."
Fia found herself at a loss for words. Seeing her struggle, Tre flashed a smile so bright it was dazzling.
"Welcome home, Fia."
"...H-Hmph... You're so unfair, Big Sis Tre... Even though you're always such a mess... at times like this... you just naturally say exactly what I need to hear most."
Tre didn't offer any lectures, nor did she ask for explanations. She simply gave a warm smile and welcomed a family member back home after a long absence.
That was all Fia needed. Wiping away the tears that began to spill, Fia smiled back.
"...I'm home, Big Sis Tre."
Thinking that she would likely never be a match for this sister of hers, Fia looked truly happy.
"...Wait, Big Sis Tre? Where are Cento and Sien?"
"Hmm... I wonder?"
"Did you slip away again? Honestly, you can't keep troubling those two..."
"No, I was just coming back to the castle for a second."
Looking at the usual Tre, Fia let out a heavy sigh and narrowed her eyes.
"...Is that so? Since you were just coming back for a second, I suppose there's no problem... In that case, you won't mind if I tell Big Sis Zwei, who's right over there."
"...Zuva-nee... might be a bit of an issue."
"Tre?"
"Hmm, Fia... could you look the other way?"
"No."
"No, huh? Figures."
In the end, Tre was grabbed by the scruff of her neck by Fia and hauled off to face Zwei. As to whether this would actually make Tre learn her lesson, it wouldn't—not in the slightest.
Extra: Various Things about Tre
Fia While the rest of the family was being considerate and holding back out of respect for Fia's complicated state of mind, Big Sis Tre didn't care about any of that. She visited the clinic constantly. Furthermore, because she ditched Cento and Sien every time, Fia was never in a position where she could turn her away.
Zwei She scolds Tre constantly. In fact, Tre is the undisputed number one in the family for the number of times and total duration of lectures received from Zwei, leaving everyone else in the dust. Despite this, she never learns her lesson. From Zwei's perspective, Tre was the first younger sister she ever had, and she dotes on her quite a bit. She just wishes Tre would show some improvement no matter how many times she’s lectured.
Kuromueina She actually dotes on Tre. While Noin is currently the youngest in the family, everyone else is quite responsible and rarely causes Kuro any trouble. While Kuro is happy that her family has grown up so splendidly, a parent's heart can feel a bit lonely when they aren't relied upon. However, Tre’s personality means she still frequently begs for things or acts spoiled toward Kuro, which secretly makes Kuro very happy. While saying things like, "Oh, I guess it can't be helped," she often grants Tre's requests.
Razulia She has excellent personality compatibility with Tre and they are very close, often causing a ruckus together.
Agni Surprisingly, they get along quite well. Since Tre has zero combat power, Agni doesn't feel the urge to challenge her to a mock battle, allowing them to engage in normal conversation.
3.4.7 Combo A dangerous combination that Kuromueina's Family is extremely wary of. It consists of the positive monster Tre, the single-minded and action-oriented Fia, and the innocent Razulia. When these three gather, there is a constant risk that they will suddenly go on a massive, unpredictable rampage.