Battle Focus is an ability that William Carter is able to use to direct his fellow Agents in combat situations during the course of The Bureau: XCOM Declassified.
This ability slows down the gameplay to a crawl and allows players to give Agents move orders or commands to attack certain enemies with gunfire or abilities.
|Spoilers for The Bureau: XCOM Declassified follow.|
Once you complete the operation by XCOM to assault Origin it is revealed that William Carter is bonded/playing host to an Ethereal. Through this bond Carter is able to more effectively direct his subordinates to action. This bond is the same kind of communication that the Zudjari are using to communicate, namely Mosaic. Dr. Weir theorizes that this communication from the Ethereal's host to those around it is what inspired Origin to use the Ethereal Shamash as the core of Mosaic.
Once Carter breaks free from his Ethereal, Asaru, it sends a telepathic message to either Director Myron Faulke, Agent Angela Weaver, or Doctor Alan Weir and forms a new bond with the character. Once this bond is formed the chosen character becomes the player's new main character, inheriting levels and abilities as well as the Battle Focus ability.
This migration of abilities as well as Battle Focus lends support many of Carter's abilities being due to his bond with Asaru.