Claymore

Claymores are the Radiant Garden's defensive system, installed presumably by Cid, who also presumably gave them their name. They aid the Hollow Bastion Restoration Committee in battle by eliminating enemies that may have infiltrated the town. The claymores can no longer assist Sora in battle after he travels beyond the Castle Gate area.

Story in Kingdom Hearts II
During the third visit to Hollow Bastion, the MCP takes control of the Hollow Bastion OS which includes the Heartless Manufactory and the town's defense system and changes the Claymore's programming, directing them to attack Sora instead.

Appearance
Claymores are spheres of light that appear from the ground. After forming a circle beneath the target, the sphere is launched up to inflict damage. The damage, unfortunately, is very minor as it can only send the target flying into the air at best which makes it a perfect target for Sora's aerial attacks.

When they begin to attack Sora, they slightly change in appearance and they also make a different sound. They still do not deal a lot of damage and they are pretty easy to dodge.

Trivia

 * In Kingdom Hearts Re:Chain of Memories, in the 13th floor and 1st basement, a system similar to the Claymores is present to attack Sora and Riku.
 * When the MCP takes control of the Claymores, their color becomes more orange than before.