AL is the artificial intelligence support system which was originally part of the ARX-7 Arbalest. AL becomes permanently locked to Sousuke after his initial use of AL during the hijacking incident. Also, because the original programmer is dead it is impossible to reprogram AL to work with anyone other than Sousuke.
At the beginning of the series AL is nothing more than your average arm slave operating system, but as the series progresses AL starts to develop a personality much to Sousuke's dismay. AL begins tuning into AM/FM band radio stations in an effort to expand its vocabulary, cultural understanding, and social knowledge. This all leads AL to occasionally attempt to tell Sousuke jokes, criticize Sousuke's own short comings, or make random exclamations and comments during the midst of battle.
During the two "End of Day by Day" novels Sousuke and AL's conflict really comes to a head and their inability to work together causes the Arbalest's Lambda Driver to become almost completely unusable. Because of this, Sousuke begins to detest the Arbalest and asks to be allowed to pilot a regular M9 during his missions. However, by the end of the two novels they were able to eventually find a mutual respect for one another and are able to operate the Lambda Driver system at a level exceeding all previous examples.
During the Novels "A Dancing Very Merry Christmas" and "Continuing On My Own" AL shows that it is now capable of preforming autonomous advanced battle maneuvers and making precision shots with the Arbalest's projectile weaponry. AL developed this ability by reviewing and analyzing all of the combat data that it has acquired while working with Sousuke over the previous 9 months.
Immediately following the final battle in the novel "Continuing On My Own", AL along with the Lambda Driver is recovered from the wreckage of the destroyed Arbalest by Wraith. Towards the end of the novel "Burning One Man Force" is is discovered that Wraith has transported AL and the Arbalest's Lambda Driver to a surviving Mithril base in Anchorage, Alaska. While there AL has worked together with Sarah Miller to design and build a whole new Arm Slave tailored specifically to match Sousuke's combat style. The new AS is called the ARX-8 Laevatein, named after a legendary sword in Norse mythology called the Laevateinn.
In the novel "Come Make My Day" AL and Sousuke have a one-on-one conversation where both admit that they have missed one another ever since the destruction of the Arbalest. By this time, AL appears to have "matured" enough to hold a personality mirroring that of Sousuke's (if the latter had grown up in different conditions); however, his jokes and comments have not lessen at all, keeping to the offbeat comedic mood of the Full Metal Panic! storyline.