Ubuyashiki Kagaya had arranged everything thoroughly for Tamayo and Yushiro.
On the west side of the headquarters, he built a separate laboratory filled with rare medicinal herbs gathered from across the country and equipped with precise instruments. He even assigned a special team skilled in handling herbs to assist with their work.
At the same time, he sent word to Kocho Shinobu, asking her to come daily and collaborate with Tamayo. Shinobu, being highly skilled in medicine and toxicology, could not only provide years of data on poisons and drugs collected by the Demon Slayer Corps but also quickly grasp Tamayo's research concepts. When the two women first met, they immediately began discussing the development of an "inhibitory drug for Muzan's cells," working together more smoothly than anyone expected.
"This is my analysis report on the blood of the Lower Moons. It records how different poisons affect demon cells."
Shinobu handed Tamayo a stack of papers, her tone serious. "But Muzan's cells are far more active than those of ordinary demons. These results might only serve as reference."
Tamayo took the report and flipped through it quickly, a faint gleam of admiration flashing in her eyes. "These data are precious—they'll save me a great deal of time. I've recently been studying a variant compound extracted from the wisteria flower. It might combine well with your poison powder and strengthen its suppressive effect on Muzan."
Yushiro stood guard at the laboratory door, watching the two women discuss with unwavering focus. Gradually, the tension in his expression eased—having such capable allies would surely make Lady Tamayo's research progress much more smoothly.
When Tomioka Giyu returned to the base, the sharp sound of clashing blades echoed from the courtyard.
He stopped at the doorway, his eyes falling on the two sparring figures, a hint of approval glinting in his gaze.
Kamado Tanjiro gripped a wooden sword, faint orange-red energy flickering around him. Each swing burned with the fiery speed unique to the Hinokami Kagura.
"Hinokami Kagura: Dance!"
The wooden blade carved a circular arc, striking straight toward Tō's chest.
Tō merged Water and Wind Breathing together, his wooden sword shimmering faintly with intertwining blue and green light. His movements retained the smoothness of Water Breathing while carrying the sharp force of Wind Breathing.
"Water Breathing, Third Form: Flowing Dance!"
"Wind Breathing, Third Form: Clear Storm Wind Tree!"
He dodged Tanjiro's slash with a sidestep and countered swiftly, forcing Tanjiro to block.
Their strikes clashed back and forth, blades cutting through the air with precision and rhythm. Both had already reached the level required for the Final Selection of the Demon Slayer Corps.
Watching them, Giyu's eyes softened slightly as memories of his own selection flashed through his mind. The corner of his lips lifted faintly.
"Stop," Giyu ordered.
Both immediately withdrew their blades and turned toward him, sweat glistening on their faces but their eyes shining brightly.
"Sensei! You're back!"
Giyu walked up to them, his tone calm. "Three days from now, I'll take you both to the Final Selection."
Tanjiro's eyes widened in surprise, his grip on the wooden sword tightening. "Really? We can finally take part in the selection?"
"Yes."
Giyu nodded and looked at Tō. "The selection is dangerous. Are you afraid?"
"Not at all!"
They answered in unison, voices filled with determination. Tanjiro wished to become strong enough to protect his family, and Tō wanted to become a swordsman worthy of helping his sensei. Neither had any reason to retreat.
Before their departure, Giyu made a special stop at Urokodaki Sakonji's residence.
Urokodaki, still wearing his tengu mask, greeted them with a gentle tone of relief. "Giyu, these are the two children you mentioned—Tanjiro and Tō, right?"
"Yes," Giyu replied, bowing slightly. "I'd like to ask you to make them fox masks."
The fox mask—perhaps it could be called a tradition passed down from Urokodaki Sakonji's lineage.
Urokodaki agreed and told Tanjiro and Tō to sit in the courtyard while he carefully observed their build and temperament. He also asked about their breathing techniques before heading into his workshop to begin crafting.
Two days later, Urokodaki handed the finished masks to them.
Tanjiro's mask was deep brown, with a small carved sun pattern at the upper right corner. Its edges were smooth, fitting his face perfectly, matching beautifully with his Hinokami Kagura.
Tō's mask was pale blue, engraved with both the windmill pattern of Wind Breathing and the flowing water pattern of Water Breathing. The two motifs intertwined—symbolizing the fusion of his breathing styles and reflecting Giyu's teachings.
"Wearing these masks means you must take on the duty of a swordsman," Urokodaki said solemnly as he looked at them. "Remember, no matter the danger, always hold on to your true heart. Never let hatred or fear consume you."
Tanjiro and Tō nodded seriously, putting on their masks with firm resolve in their eyes.
After leaving Urokodaki's home, Giyu didn't return right away. Instead, he took a detour to the clearing where he used to train.
It lay halfway up the mountain, surrounded by pines, with a massive boulder standing in the center—the very same one he had once used to hone his blade alongside Sabito.
The rock still bore countless sword marks, some deep, some shallow, each a record of sweat and effort from those days.
Giyu walked up to it and gently traced his fingertips across the cuts. Memories of Sabito surfaced unbidden in his mind—the boy behind the fox mask who always smiled and encouraged him, the companion who had sacrificed himself during the Final Selection to protect others.
"Sabito, Makomo…" Giyu whispered softly, a faint ache welling in his chest.
He stood there quietly for a moment, then steadied his emotions and turned to leave. He still had things to do—he couldn't stay trapped in the past.
"Giyu."
A familiar voice came from behind him—light as the wind yet unmistakably clear.
Giyu froze mid-step, his whole body tensing.
That voice… it was too familiar, so familiar that his heart clenched violently.
He turned around slowly.
On the massive boulder sat a boy wearing a fox mask. A carved scar marked the right side of the mask's face—exactly the same as the one in Giyu's memory. His light orange hair glowed softly under the sunlight. He wore a faded training uniform and held a wooden sword, sitting quietly and looking straight at Giyu.
Even through the mask, Giyu recognized him instantly—it was Sabito.
The companion he thought he had lost forever. The boy who had once given him courage and warmth when he was young.
Giyu's pupils shrank sharply. His breath caught. His throat felt blocked, unable to form a single word.
How could this be? Sabito had died in the Final Selection. Why was he here? Was this an illusion? Or… a Blood Demon Art?
The boy on the rock spoke lightly, almost teasing. "Giyu, did you forget your fellow disciples after becoming a Hashira?"
Giyu stammered in disbelief. "You… are you Sabito?"
The boy jumped down from the rock, calm and composed, and as he came closer, Giyu noticed he was actually a head shorter than him.
Then the boy reached up and slowly removed his mask.
A gentle smile appeared before Giyu's eyes.
"Long time no see."