The Brave Heart is the Emblem Frame of Kazuya Shiranami that had the ability to combine with the other NEUE Emblem Frames and serves as an amplifier to aid the angels in battle. On it's own however, it does not technically count as an Emblem Frame as it does not function off the H.A.L.O. System.
In the Galaxy Angel II Trilogy, the Braveheart's survival (as well as that of the Luxiole functioning as the second trilogy's version of the Elsoir) is a key objective in every mission.
From the Braveheart, Kazuya can select one of the Rune Angel Wing members to merge Emblem Frames with to boost their capabilities. In combat it can manually shoot at the enemy ship's guns and destroy their armor and offensive cannons. This causes the special meter to fill up quicker than normal but damage received is also amplified.
Kazuya can also accelerate a chosen Emblem Frame to reach the target quicker and request repairs with a quick command.