The sun rose and fell. The seasons turned. The clearing in the woods saw it all.
A boy, now fourteen, swinging a black sword. A thin line of blood colored its edge. He cut a tree. It was a good cut.
The same boy, now fifteen. His body was harder. His swings were faster. The red on his blade was brighter, thicker. He could cut through three branches with one swing. The air hummed with the power.
The boy at sixteen. He moved like water. His black sword was a blur of red. He could make the blood wrap around the blade in sharp points. He practiced for hours, until his clothes were stained and his arms shook. He never complained. He never seemed to get tired.
Jin watched. He was getting older. His own body ached. But he saw the monster he was creating. A perfect, emotionless weapon.
At seventeen, Tsuruji learned the Fourth Form: Sanguine Whip. He flicked his wrist. A rope of his own blood, sharp as a razor, shot from his hand. It cut a distant tree, then snapped back. The recoil was brutal. It left a red mark on his arm. Tsuruji just looked at it. Then he did it again.
The final year. Tsuruji was eighteen. A man. His face was hard. His eyes were still empty pools.
In the clearing, Jin faced him. "Show me the Ninth Form. Bone-Chilling Sacrifice."
Tsuruji nodded. He took a deep breath. His body went still. Then, the veins on his arms and neck stood out, dark against his skin. His muscles tightened, coiling with terrible power. The air around him grew hot. His black blade glowed a furious, burning red.
He moved. He was not a blur; he was a ghost. He crossed the clearing in less than a second. He swung his blade.
A massive oak tree at the far end of the clearing shuddered. Then, with a sound like thunder, it split straight down the middle. Both halves fell to the ground, shaking the earth.
The red glow vanished from his blade. Tsuruji stood, his chest heaving. His body was whole, but the cost was written in the tight pain around his eyes. A normal man would be screaming. Tsuruji just breathed, mastering the agony, locking it away in the same void as everything else.
Jin walked over to him. He looked at the fallen tree. He looked at the young man.
"There is nothing more I can teach you," Jin said. "The Final Selection is in one week. Go. Become a Demon Slayer."
Tsuruji sheathed his pure black sword. He gave a single, sharp nod.
He was ready.