Someone climbs onto the roof from the ground when dawn comes to proclaim that a new day has begun! They proclaim this at the top of their lungs!
The thing that climbs up on the roof to proclaim that the new day is here is a centaur (せん). Ohoho, did you think I was going to say it was a rooster? Wrong! Centaurs are taller than humans and roosters, so when they climb onto the roof with their horse legs they can see dawn starting before anyone else.