Yoriichi found out his brother turned into a demon but didn't want to kill him so he put a bamboo muzzle over his mouth so it would hold back his bloodlust for eating humans. It worked but yet he still drooled around humans. Yoriichi always held Kokushibo in a box on his back since demons couldn't go out in sunlight.

Yoriichi walked out the city at night while his brother slept a bit in the box then when he sat down, Kokushibo crawled out.