Horizon is a company in the world of killer7. It is owned by Curtis Blackburn, who used it to strike a deal with the Opposition Party which allowed him access to orphans from the Immigration and Naturalization Service.
Horizon is only mentioned briefly in Hand in killer7 and is never mentioned in the main game. However, it is very notable to the development of the game as a cut mission took place at their building, the Temple of Horizon/Horizon Tower. The Tower featured very prominently in trailers for the game and was used in a variety of circumstances, such as an alternate way of exploring Dan Smith's past with Curtis Blackburn. Sundance Shot was also to appear here at some point. In a later version of the game, the mission at Horizon was instead to assassinate Steve Thunderson, and took place between Target03: Encounter and Target04: Alter Ego (pushing the assignment number of Target06: Lion up to 44).