The game is set in the Erebonian Empire and takes place after the Trails in the Sky trilogy and concurrently with Trails from Zero and Trails to Azure.
The game's plot is centered around Rean Schwarzer and his fellow students of "Class VII" at Thors Military Academy, a newly formed class composed of both Erebonian nobility and commoners and the only class at the academy that does not segregate based on social class. The story follows Class VII throughout the school year, focusing on their field studies that take them to various cities and areas across Erebonia. The primary purpose of doing so is for the class to witness first hand the reality of the Empire, as the power struggle between the aristocratic Nobles that command the Provincial Army, and the working class Reformists led by Chancellor Giliath Osborne threatens to lead to civil war. At the same time the students increasingly come into conflict with a terrorist group later known as the Imperial Liberation Front(with the Noble Alliance secretly backing them), led by the masked but charismatic leader known only as "C". They are also investigating their academy's old schoolhouse which mysteriously grows and changes its layout every month.
The game has a new battle system, designed for commands in fights to be selected at a faster rate. The system allows players to pair characters up with a "Link" system, which allows follow-up attacks and provides various other benefits. Links becomes a more useful asset to the player as the story progress and characters level up their "Link Levels" with other characters[2] Cold Steel maintains the "AT" (Action Time) battle system, which displays ally versus enemy turns on a bar on the screen. The Orbment system from past games has been streamlined. Trails of Cold Steel inherits the "Master Quartz" system from Trails to Azure.
Source: Wikipedia, "The Legend of Heroes: Trails of Cold Steel", available under the CC-BY-SA License.