Sora spots his first Soldier when he enters the Second District, as an exhausted man is caught by the Heartless and has his heart stolen. The heart is transformed into a Soldier Heartless, which escapes through a Corridor of Darkness. A platoon of Soldiers later lays siege to the Hotel in which Sora, Donald, Goofy, Leon, Yuffie, and Aerith are discussing the situation, and Leon helps hold them off so that Sora can escape and find the leader of the local Heartless, the Guard Armor.
Kingdom Hearts II
As Sora first returns to Hollow Bastion, a troop of Soldiers run past. Later on, another swarm steals the 100 Acre Wood novel, damaging it and shunting Sora back out of it. Sora defeats them and retrieves the book, returning it to Merlin and going out to retrieve the stolen pages.
Soldiers have a much more refined appearance than Shadows, appearing as a noble knight-type warrior at first glance. A closer examination reveals the Soldiers are just as beastly as the other Heartless. Their muscular forms are clad in a bluish-black body suit bearing the Heartless emblem and purple inverted emblems trimmed in gold on the knees. They wear black, silver trimmed shoes that end in spiral toes, silver wristbands, and a silver knight's helm decorated with two angular, eye-like spirals on the front and a yellow stripe at the base of the curled silver plume. Its true Heartless behavior comes out on a close examination of their fierce blue and red-tipped claws, and their shadowed faces with bright yellow eyes and toothy maw.
The Soldier's name references soldiers serving the military. This highlights the Heartless's battle capabilities. They also appear in large numbers, referencing an army. This is reflected in the names of its variants, such as the Sergeant and the Commander.
Kingdom Hearts II
Kingdom Hearts 358/2 Days
Soldiers have a fairly predictable pattern of running around and stopping, or if close enough to the target it will run to the target and stop before using one of its attacks. Both of its attacks have a delay before hitting the target, making it easy to react to. Blocking its kick attack will cause it to fall over, allowing more damage to be dealt.
Kingdom Hearts III
Notes and references