Half a year had passed since that incident.
Kaina was currently recuperating at our estate. Though she still suffered mentally from the trauma, she had refused the new President's suggestion to retire. She vowed that she would never let others experience the horrific things she had seen and endured. Instead of leaving the Hero world, she decided to take a short leave of absence before returning to the field.
I worried she was pushing herself too hard, but I respected her resolve.
"An opening!"
I was broken out of my thoughts by Momo and Himiko charging at me. Momo lunged forward with a practice blade, while Himiko unleashed a flurry of threads. Both had been training under me, receiving my Breathing Styles through intense daily sparring sessions.
Fortunately, Momo's constitution was a perfect match for Moon Breathing. I have been teaching her forms one through six. Beyond the Sixth Form, the style transforms into supernatural swordsmanship that scatters physical crescent moon blades or generates slashes without the blade even moving—techniques impossible for someone without centuries of demonic evolution. Thus, we stayed within the first six forms for now.
Himiko, however, didn't quite suit Moon Breathing. Instead, she developed her own unique style: Spider Breathing. It utilized her Blood Demon Art and a high-level stealth technique that allowed her to hide her presence and slip into the opponent's blind spots.
"Moon Breathing, First Form: Dark Moon, Evening Palace!"
"Spider Breathing, First Form: Cutting Thread Cage!"
Their combined assault rushed toward me, but it was futile.
"Moon Breathing, Eighth Form: Moon-Dragon Ringtail."
With a powerful horizontal sweep, I unleashed a massive slash that countered Momo's Dark Moon and severed Himiko's threads in an instant.
"Moon Breathing, Second Form: Pearl Flower Moons!"
"Spider Breathing, Second Form: Murderous Eye Basket!"
"Moon Breathing, Third Form: Loathsome Moon, Chains!"
I stepped back, cutting through their techniques before launching my own counter-offensive.
"Moon Breathing, First Form: Dark Moon, Evening Palace."
The wide horizontal slash forced them to take a defensive stance, but they were still blown back. Both suffered deep cuts that would have been fatal to a human, but their wounds closed almost instantly.
Since receiving a heavy concentration of my blood, both of them possessed absurd regenerative capabilities. I discovered during an experiment a few days ago that my own regeneration has reached the level of the progenitor, Muzan. When I cut my own arm, the skin knitted together faster than the blade could pass through, making it look as though the steel simply ghosted through my body.
"Hmm... You are both still far from reaching the Transparent World..."
I wanted them to manifest the Marks, the Bright Red Blades, and the Transparent World. Even though they had become strong enough to easily suppress average Villains or Heroes, they were still beginners who had only been training for six months. I didn't expect them to master the three ultimate techniques so quickly; if it were that easy, the original Demon Slayers would have wiped out all demons in a single generation.
"Haah... haah... I need... to steady... my breathing..."
"Phew... I have to... become as strong... as Brother..."
Despite being Demons, they were panting heavily, sweat pouring off them. My training sessions were, quite literally, murderous. If a human had attempted this regime, they would have been turned into mincemeat or died of exhaustion long ago. Every spar was conducted with real blades and a genuine intent to kill, and every breathing exercise pushed their lungs to the point of rupturing.
The reason I drove them so hard was for their own protection. I cannot be with them twenty-four hours a day. They must be able to defend themselves and strike back. Thanks to this, they had reached a level of skill comparable to a Hashira within six months, but it still wasn't enough.
Breathing is a form of physical enhancement, a "buffing" technique. It alone cannot defeat Villains with reality-warping or extreme physical Quirks. That is why I made sure they also mastered their Blood Demon Arts.
"That is enough for today. Prepare yourselves for school."
"Haah... haah... yes..."
"I can't... move another inch..."
Momo and Himiko collapsed onto the floor, their bodies practically protesting the intensity of the workout. Seeing these world-class beauties sprawled out on the dojo floor made me feel a pang of guilt, but Demons do not grow without such hardship.
"Here. Take some water."
I handed them chilled bottles. My conscience demanded at least this much. They took the water and began to recover their strength.
"Thank you, Michikatsu."
"Heehee, thanks, Brother!"
"You have both progressed significantly... but do not grow arrogant. You have yet to even graze my robes."
My goal was for them to surpass the Hashira of the golden age. Only then would I feel at peace.
"Ever upward! I will keep it in mind!"
"I really admire your energy, Momo. I don't even have the strength to speak..."
"Oh, Himiko... in that case, perhaps you should hand over the title of 'Upper Rank One'?"
"No way, Momo. That rank represents that I am Brother's number one, doesn't it? I'm not giving that up."
Momo's smile remained, but the light in her eyes sharpened.
"Oh? Michikatsu's number one? Surely that would be me. We are childhood friends and betrothed, after all."
"Ara... but Brother and I are family. We might not share blood, but our bond is official. Plus, I was the first one to receive his 'blessing'—his blood. It's only natural that I am the first."
"Is that so~?"
"Nng~?"
Zap—!
Static seemed to crackle between them as they glared.
"Sigh..."
The usual catfight. It was exhausting. Usually, they were as close as real sisters, but the moment I became the subject, they turned into snarling rivals.
"Enough... you are taking the jest too far."
"Michikatsu?"
"Brother?"
"Behave yourselves."
"Yes... we're sorry..."
At my word, they both bowed their heads in contrition. I don't mind a little bickering, but I won't tolerate a genuine rift between them.
After showering and changing, we left the estate. Today wasn't for school; I was escorting them to the UA High School Entrance Exam. Knowing how hard they had worked to prepare for Japan's premier hero academy, I came along to support them.
I wasn't taking the exam myself. I was joining UA not as a student, but as a teacher. As a registered Pro Hero, I couldn't realistically enroll as a student in a hero-training program. However, I didn't want to be separated from Momo and Himiko. The President had written a recommendation letter, and UA's principal, Nezu, had agreed to appoint me as the youngest faculty member in the school's history.
"Still, it's strange to think of you as a teacher, Brother."
"It feels a bit awkward, doesn't it?"
"It cannot be helped... a Pro Hero cannot be a student."
The principal had argued it would be unfair to the other students, and I agreed.
"However... we shall still see each other daily. Do not let it weigh on you."
I patted their heads. Both of them smiled and leaned into my touch.
"Hey, look over there..."
"Whoa... is that his girlfriend? Both of them? I'm so jealous..."
"But look at the guy. He's terrifying."
The passing crowd whispered about us, but I ignored them completely. I was used to it.
"Go on, then. I shall be waiting."
I stole a kiss from each of them before they headed inside. They both looked like they were melting as they answered.
"Yes~ ♥"