Five months passed in the blink of an eye.
The first month Kagerou spent with the Rengoku family was nothing but awkwardness.
How could it not be? A new world. A new body. No memories to anchor himself.
Though his frame was that of a four or five-year-old child, his consciousness remained that of someone closer to twenty. A strange, dissonant existence.
At first, his body was frail, malnourished, skinny to the bone. He didn't know what had happened to the original owner of this body, but within a month of eating proper meals at the Rengoku household, his health returned. He began to look like a normal child his age.
By the second month, Shinjuro had begun training him. Only the basics, of course, running, stretching, and building stamina.
"We can't start the real thing until your body can handle it," Shinjuro had said. But as a Hashira, he was constantly leaving on missions, and so the "real thing" never came. Still, Kagerou didn't complain. He understood. Everything has its time. For now, the basics were enough.
And the results spoke for themselves. Five months in, his body had changed. With the natural growth of a child and the discipline of his training, he had become stronger, stronger than most children his age by far.
But the most interesting change came not from training, but from family.
By the third month, with Shinjuro away on missions and Ruka often occupied with the household, it fell to Kagerou to care for little Kyojuro. Day after day, month after month, the baby was always by his side.
And somehow… something happened.
Little Kyojuro grew so attached to Kagerou that both Shinjuro and Ruka couldn't help but feel a little jealous.
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- Back to the third month of Kagerou's stay in the Rengoku household.
By then, he had already realized what it truly meant to be a Hashira.
It wasn't freedom, it was responsibility doubled.
Shinjuro, especially, was rarely home. Almost every night he left for missions, returning only at dawn. Sometimes he wouldn't return for days. In those three months, the Rengoku residence was usually left with only three people: Ruka, Kagerou, and little Kyojuro.
There were no servants. No attendants. Demon Slayers lived in secrecy. Kagerou had learned that the Corps, despite its strength and duty to protect humanity, was an illegal organization, unrecognized by the government. To the common people, demons were nothing more than superstition.
At first, this had surprised Kagerou. But he quickly understood. If the existence of man-eating demons became common knowledge, the world would drown in panic. Fear would never end.
And so, demons lived in the dark, and the slayers hunted them there.
But today was different. Today, Shinjuro had no mission. A rare day of peace.
Sensing this, Kagerou volunteered to watch over little Kyojuro so that Ruka and Shinjuro could finally enjoy some time together.
Under the shade of a tree, Shinjuro rested on Ruka's lap, half-dozing as his wife stroked his hair. Together, they watched Kagerou in the garden, holding little Kyojuro's hands, guiding the toddler's shaky steps.
"You know, Shinjuro-san," Ruka murmured, her eyes soft but troubled. "Sometimes I ask myself if Kage-kun is really just a child"
Shinjuro cracked an eye open. His gaze followed hers to where Kagerou patiently guided the baby. "…Why? We already knew he was too mature for his age. Why be surprised now?"
"Too mature," Ruka repeated. "In these few months, all he's done is train, help with chores, and take care of Kyojuro"
"Isn't that a good thing?" Shinjuro frowned. "He's living a normal life"
Ruka shook her head immediately. "No. A child his age should be outside, laughing, playing with other children. That's what we call a normal life"
Shinjuro fell silent, then sighed. "With what he's gone through… with a mind that grown-up in a body that small… do you really think he can make friends like other children?"
"But still-" Ruka began.
"Just let it be." Shinjuro's voice was quiet, but firm. "Everyone has their own pace. Kage does too. If he can't find friends, then we'll fill that hole. We'll be his parents and his friends. And he still has Kyojuro. Or… maybe we should make him anoth-"
Shinjuro stopped mid-sentence.
Because at that exact moment, Kagerou came running toward them, little Kyojuro cradled in his arms.
"Mother! Shinjuro-san!" he called urgently.
Both parents bolted upright, alarmed. They feared something had happened to their baby, but the words that came next left them speechless.
"…Look!" Kagerou's face lit up as he held the toddler forward. "Kyojuro just said his first word!"
He turned the baby's face toward him, smiling brightly. "Kyojuro, do it again!"
Little Kyojuro's eyes sparkled. As if he understood, he flailed his arms happily, giggling. Then-
"…Nii! Nii!"
Shinjuro and Ruka froze.
'Nii!?'
Their one-year-and-three-month-old's very first word… wasn't "Papa" or "Mama"
It was "Nii," Big brother.
Shinjuro and Ruka's thoughts collided in perfect unison:
'Why him?!'
And from that day forward, both parents found themselves secretly jealous of Kagerou.
Thus began an unspoken competition within the Rengoku household. Since first place had already been claimed by Kagerou, the proud recipient of Kyojuro's very first word, the battle between Ruka and Shinjuro became one for second place.
Whenever Shinjuro returned home without a mission, he would crouch in front of his son and firmly say, "Papa. Say Papa." And whenever Ruka had a moment while playing with Kyojuro, she would lovingly whisper, "Mama. Come on, Kyojuro, say Mama"
But fate, and free time, were on Ruka's side. As a full-time housewife, she spent nearly every waking moment with her son. Shinjuro, no matter how fierce and stubborn as a Hashira, simply could not compete with her constant presence.
In the end, Ruka proudly secured second place when Kyojuro finally called her "Mama." Shinjuro only earned his long-awaited "Papa" a month later. Though technically defeated, he couldn't help but feel his heart swell with pride.
And so, in the Rengoku household, their everyday battles were not fought with swords or demons, but with words, smiles, and the laughter of a growing child.