whistle

An aerodynamic whistle (or call) is a simple aerophone, an instrument which produces sound from a stream of gas, most commonly air. It may be mouth-operated, or powered by air pressure, steam, or other means. Whistles vary in size from a small slide whistle or nose flute type to a large multi-piped church organ.

is a Japanese manga series written and illustrated by Daisuke Higuchi, which was adapted into a 39-episode anime television series, broadcast exclusively by Animax across Japan and South Korea.