Basically, it's a retanking of some chapters from Full Metal Panic!. It's sort of like FMP! Fumoffu.. meaning that there's no mecha plotline, only short stories. Also there's an extra story not presented anywhere in each volume of this series.
(Source: Mangaupdates)

When an unknown Arm Slave surfaces somewhere in the Taiwan Strait near mainland China, MITHRIL orders Melissa Mao and her team to go into a divided Hong Kong to investigate the perpetrator of the unknown Arm Slave. As the team continues to check into the reports of the unknown Arm Slave, the culprit is believed to be a potential SRT recruit back from Sousuke's training days in Belize when he was not recruited by MITHRIL.

A sergeant by the name of Sousuke Sagara is assigned an important task. That of guarding high school girl Chidori Kaname. Sousuke is a military genius, gaining high rank at an early age, but because of his strange upbringing, he lacks social skill. Now, he finds himself as a fish out of water as he attempts to protect a girl from an evil organization and turn in his school work on time.
(Source: ANN)

Seiya was forced to accept an invitation to an amusement park by the mysterious and beautiful girl Isuzu. What he didn't know was that she would bring him to the decrepit Amagi Brilliant Park, Japan's most disappointing amusement park. Seiya is introduced to the leader of the Park, the "real princess" Latifa, who suddenly entrusts him with saving the park, which is in danger of shutting down. Amagi Brilliant Park, it turns out, is not just any amusement park, but rather one populated by fairies.

(Source: ANN)

Following the Tuatha de Danaan's seajacking incident, things are back to normal at Jindai High School in Tokyo, or as normal as they get with Sousuke guarding Kaname. After finding out who betrayed Mithril and caused the seajacking incident, Kurz and Mao are sent on a top secret mission in order to capture and bring the traitor back.

However, Sousuke and Kaname's lives are about to change when they meet Leonard Testarossa, a high ranking member of a mysterious group named Amalgam. After their meeting, Leonard warns her that he would do anything to recruit her even if it means war in the streets of Tokyo.

Sosuke has finally lost his mind - and his memory! Rehashing his previous exploits will keep Kaname busy, but it doesn't take long for the military mind of this soldier to bounce back with a bang - literally! He's locked, loaded, and back to his old self by first period, as bombs and bullets grace the halls of high school!