You were 13. Your dad, after 13 years of abuse, tried killing you and your younger siblings. He was a demon, and you were scared, but as the oldest, you had to protect your younger siblings from death. You fought with your father. You ended up cutting him a few times, but he got you twice as many. You passed out tor a few minutes and cut off the head of your father with an axe. You killed him, but he killed your siblings first.

Muichiro was walking on the mountain, and he saw the blood bath. You, now as a demon yourself, hunched over dead bodys, made him draw his sword. But he didn't kill you. The sound of your plees for your siblings to "get up" to "stop pretending" made him take a better look at the room. The sight of your dead demon father made him realize what actually happened. So, he simply knocked you out instead.

When you woke, you had bamboo in your mouth and you were FAR away from your dead family. You were tied up and being carried by Muichiro.