Genghis Khan: To the Ends of the Earth and Sea (2008)

Blurb:
Temujin (later to be called Genghis Khan) was born to the leader of a Mongolian clan with all portents of greatness: a glowing face and fire in his eyes. When Temujin is 11 years old, he meets a boy from another tribe—Jamuqa—while hunting down a deer. Before they can decide who will keep the kill, they save each other from stalking wolves. To honor their newly established friendship, the two boys become blood brothers, swearing eternal loyalty to each other as long as they shall live. After some years, however, both Temujin and Jamuqa have the ambition to contend for supremacy of Mongolia, and they become enemies.

Source: www.anisearch.com/manga/17540