The moment I opened my eyes, something was wrong. The ceiling was the familiar wooden beam of the Butterfly Mansion. White plaster walls. Morning light streaming through the window. All sights I'd seen countless times before—— My chest felt heavy. With a hazy head, Tanjirou touched his own chest. My fingertips hit something. "……Huh?" A voice came out. A high voice. "……What?" I murmured again, checking my own voice. Still high. Like someone else's voice entirely. Tanjirou sat up slowly and looked at his own palm. Small. White. Not Tanjirou's hand. A small mirror hung on the wall—one of the Butterfly Mansion's fixtures for injured patients to check their condition. When Tanjirou saw the face reflected there, he nearly screamed. It was a girl's face. Soft black hair spread across the pillow. Clear green eyes wide open blankly in the mirror. The birthmark on his forehead was still there. Fox-ear-like hairpins hung there somehow. Tanjirou clenched his back teeth. Swallowed the scream. Calm down. Just calm down. One deep breath. Air into the lungs, exhale slowly. Total Concentration Breathing——no, just a regular deep breath. Tanjirou looked at the mirror again. (I am Kamado Tanjirou.) He told himself in a proper male voice inside his head. Even if the body changes, that doesn't. I am Kamado Tanjirou. Born to a charcoal-burning family, my family was killed by demons, and my only surviving sister Nezuko became a demon herself. I joined the Demon Slayer Corps to turn Nezuko back human, honed the Water Breathing, and now I continue fighting as a Pillar trainee. That's who I am. The body just changed. "I am Kamado Tanjirou." I said it out loud. A high, cute voice came back. Not convincing at all. Tanjirou sat on the edge of the bed and held his head. The Butterfly Mansion——the medical and recovery base of the Demon Slayer Corps managed by the Insect Pillar, Kocho Shinobu. A place for injured soldiers to recover, and Tanjirou had recuperated here many times. Usually it's a place where I can feel safe, but not this morning. Anyway, I need to get to the hallway. I need to check if only I changed like this, or if someone else did too. --- In the hallway, the wooden floor still held the morning chill. Beyond the shoji screen, the medicinal herb garden was visible. Wisteria flowers swayed in purple. A sweet wisteria scent drifted over. Tanjirou paused there for a moment and breathed it in. No reason. It just felt calming somehow. Then. "[excited]Delicious! So delicious!" A bright voice came from the kitchen direction. But——the voice was high. Tanjirou tilted his head and peeked into the kitchen. There was a woman with her kimono sleeves rolled up. Wearing black hakama, sitting boldly in front of a table, shoveling down a massive pile of white rice at incredible speed. But that eating style looked familiar. An overwhelming eating style. Completely unrestrained, bold eating. "[surprised]……Rengoku-san?" The woman turned around. Large eyes gleamed. "[excited]Tanjirou boy! Look! The food is delicious! When food is delicious in the morning, people gain energy!" No doubt about it. Rengoku Kyojuro. His body had become female, his voice had become high, but he didn't seem to care at all. His eyes sparkled in front of the mountain of white rice. Tanjirou felt conflicted. This person is amazing, he thought honestly. When I returned to the hallway, someone was standing by the window. A woman with long black hair, looking out at the medicinal herb garden. Her posture was perfectly straight, unmoving. Tanjirou called out softly. "[gentle]……Tomioka-san?" The woman turned slowly. A cool face. Expressionless. But her eyes clearly reflected Tanjirou. She nodded slightly. Nothing said. Just like always. Tomioka Giyu——the Water Pillar. The master who taught Tanjirou Total Concentration Breathing. Even with a female body, even brushing back long black hair with one finger, that silence hadn't changed one bit. Tanjirou felt a little reassured somehow. Then. Footsteps echoed from deep in the hallway. "[sad]Big brother……" A low voice. Tanjirou's eyes widened. Nezuko came running. But——Nezuko now had a boy's body. A low voice. Only those round eyes remained the same, and she approached Tanjirou with a troubled expression. "[sad]I feel weird" Nezuko's voice was low. A boy's voice. Tanjirou's brain couldn't quite keep up with that voice coming from Nezuko's mouth. "[serious]It's okay. I'll definitely turn us back to normal." I said it. I meant to say it powerfully. But Tanjirou's voice was high and cute. Nezuko stared at Tanjirou. "[gentle]……Big brother's voice is cute" "[angry]It's not cute!" I yelled in a cracked, high voice. Not scary at all. Nezuko laughed a little. Tanjirou felt even more frustrated. --- The Butterfly Mansion's great hall. A spacious room of thirty tatami mats, filled with everyone who could gather. Rengoku had brought white rice again. Tomioka Giyu stood by the window. He seemed to like the outside. Nezuko sat next to Tanjirou. Murmured "big brother" again in that low voice, and Tanjirou felt a little melancholy again. The problem was not knowing who was who. Everyone's body had changed. Different faces. Different voices. Even if they said "I am ○○," no one believed them. Because everyone was saying the same thing. "[excited]It's Rengoku! Rengoku Kyojuro! You can tell, right!" Rengoku stood up and waved his arms wide. Female body, high voice, but the attitude was perfectly Rengoku. Everyone looked unconvinced. Giyu remained silent by the window. He wasn't naming himself at all. Someone said, "So how can we confirm?" Silence spread. Tanjirou thought for a moment and raised his hand. "[serious]……I can judge by scent" Everyone looked at Tanjirou. Tanjirou stood up and approached each person. Sniffed. He remembered the scents of his comrades from fighting as a Demon Slayer. "[serious]Rengoku-san smells like fried food and charcoal. No doubt about it" Rengoku puffed out his chest. "[excited]That's right! Rengoku Kyojuro! Proven!" "[sarcastic]……Being identified by scent is a complicated feeling" He added that with a complicated expression. Tanjirou approached Giyu next. "[serious]Tomioka-san always smells like water. The scent of someone who uses Water Breathing" Giyu remained silent even hearing that. But when Tanjirou approached, he——just slightly, just barely——seemed to turn toward Tanjirou. It might have been his imagination. Tanjirou moved on to the next person without noticing. During the meeting, things gradually came together. Organizing the current situation——everyone's body had changed. The cause seemed to be something they inhaled while sleeping. But no one saw anything like that. Something happened during the night. The Demon Slayer Corps is an organization that fights demons that eat people. Led by the Ubuyashiki family for generations, a group of swordsmen unrecognized by the government, and Pillars like Tanjirou are the strongest nine——swordsmen at the peak of each breathing style. They should be able to defeat any number of ordinary demons, yet this morning they were in complete chaos. Did a demon do this? No answer came. No one knew how to turn back either. The meeting ended without deciding anything. Tanjirou suddenly noticed. Giyu had moved to the seat next to Tanjirou at some point. But Tanjirou didn't notice. Only Rengoku grinned. --- After the meeting, Tanjirou went alone to the training grounds. A dirt plaza in the Butterfly Mansion's courtyard. Soft midday sunlight streamed in, and the scent of wisteria flowers drifted from the medicinal herb garden. Tanjirou held his Nichirin sword. The Nichirin sword——made from special iron mined from Yoriichi Mountain, only this could sever a demon's neck. Tanjirou's sword had taken on a reddish hue in response to his breathing. I took my stance. Used Total Concentration Breathing. Took in massive amounts of air to boost physical ability. That's the basic principle of a Demon Slayer. Water Breathing, First Form——Water Surface Slash. I swung. My balance collapsed. Tanjirou's body had changed to a female form, and the center of gravity was in a completely different position. The muscle distribution in the arms was different. Lung capacity had changed. The moment I swung the sword, my entire body felt scattered, and Tanjirou fell spectacularly. Rolled across the dirt. The Nichirin sword flew from my hand. The blade arced and drove forcefully into the wisteria trellis in the medicinal herb garden. The wisteria flowers swayed. Purple petals fluttered down. Tanjirou sat on the dirt and watched the falling petals blankly. "……The center of gravity is completely different" I murmured in that high voice. Now I understood. When your body changes, all the sensations you've built up over years shift completely. The breathing volume changed. The power in the arms swinging the sword changed. The way the feet stepped changed. How long did it take to master Water Breathing? Every single day under my master's guidance, practicing, letting it soak into my body——and now I can't use any of it. (If I can't turn back) Something frightening slowly spread through Tanjirou's chest. (I won't be able to protect Nezuko) Nezuko was still a demon. Tanjirou continued fighting to turn Nezuko back human. He honed Water Breathing for that. He became a Pillar trainee for that. All of it——I can't use it in this body now. I looked at my hand covered in dirt. Small and white. How long would it take to be able to swing a sword with these hands again? Then. "Caw-caw-caw!" A bird's cry came from the direction of the Butterfly Mansion's gate. A Kasanegui crow——a messenger crow used by the Demon Slayer Corps. Tanjirou ran to the gate. Covered in mud. A black crow perched on the gate pillar and cried out in a shrill voice. "Message From Ubuyashiki Estate! Sleep Smoke Damage Reported Elsewhere Too! Traces Of The Demon Responsible Found In Northwest Forest!" Tanjirou clenched his fist. With muddy hands. "[serious]I have to go" I said. But my feet stopped for a moment. That fall from earlier came back. Falling spectacularly, the sword flying, wisteria petals falling. That sensation. How could I fight a demon with a body where I can barely use breathing properly? No answer came. Evening light painted the Butterfly Mansion's roof orange. Wisteria flowers in the medicinal herb garden swayed in the breeze. A crow cried somewhere again. Tanjirou, covered in mud, slowly looked up at the sky. The sky was vast and beautiful. With no answer, the day came to an end.