Capítulo 1477: Foundation Of Supremacy.

The last training objective is the dragon's domain. It involves creating a domain around them with dragon force. Ambient mana is subjugated to their will through the use of dragon force. This prevents mana from being used by others and can magnify their dragon tongue. 

Unlike dragon tongue which can be brute forced, dragon's domain is a challenge in the manipulation of dragon force. A dragon's domain is meant to suppress mana within it so that no one else can manipulate it. But this suppression is not absolute, like the dragon tongue. When two dragon domains clash, it is the dragon with the stronger and better control of the dragon force that wins.