Ace Combat Xi: Skies of Incursion was the only iOS game in the Ace Combat series for Apple devices (iPhone, iPod Touch, and iPad). It was released on December 3, 2009 through the App Store. It received updates sporadically, mostly to add more aircraft.
The plot of Ace Combat Xi followed the Aurelian Air Force Falco Squadron during the opening stages of the Aurelian War as Leasath begins its invasion of Aurelian territory. Xi serves as a prologue to Ace Combat X: Skies of Deception, which had started off mid-way through the war after Leasath had defeated most Aurelian forces.
In 2013 and 2014, the game's description in the App Store was updated to note that save files were not functional in iOS 7 or iOS 8, respectively. By March 30, 2015, the game was removed from the App Store and all in-app purchases were disabled. In addition, the official website was also taken down.
In 2020, Aurelia is suddenly invaded by its northern neighbor, Leasath, who successfully establish a foothold within Aurelia's northern territory. Using this to their advantage, Leasath forces begin a massive offensive to capture Griswall, Aurelia's capital city. Phuku Lagolla Air Base, located to the southwest of Griswall, orders Falco Squadron to fend off invading forces.
Ace Combat Xi plays very similarly to Ace Combat X: Skies of Deception. Players engage and destroy enemy targets on both land, sea, and air using the Multi-Purpose Gauge to determine the strength of enemy forces or damage to allied forces.
Ace Combat Xi features three difficulty levels: Easy, Normal, and Hard. These affect the number of enemies in a mission, how smart their AI is and how much damage the player can take.
- Including the special mission added in v1.1.1, Xi only featured nine missions, the lowest count in any Ace Combat game. The next-lowest is Ace Combat: Northern Wings, with 10 missions.
- It is likely that iOS 9's release in late 2015 and the game's issues in iOS 7 and iOS 8 prevented Apple from permitting Xi from being sold any further. However, no official statement has been made.