Reclaimer is a music piece featured in Halo 2, and it is present on Volume 2 of the Halo 2: Original Soundtrack.
The piece is a remix of the track Unyielding, featuring the guitar playing of Steve Vai over Unyielding's fast paced piano work.
It's heard at the start of Quarantine Zone, during the fight where Flood-driven vehicles are introduced.
It almost has the same rhythm as Rock Anthem for Saving the World and you can hear some piano sounds.
List of music heard in the Halo series