Rare Suit, like all other Shingu, was created four hundred years before the start of the series by The Emperor of that time in an attempt to create weapons that could surpass the Teigu.
It was kept hidden in the Empire's secret storage until It was given to Guy by Gozuki. Its status is currently unknown after Guy was killed by Weneg inside the gravekeepers' tombe, which collapsed shortly afterwards.
Rare Suit's ability is manipulating soil. It is unable to create soil out of nothing. Its biggest advantage is burrowing underground, which can be used to surprise attack unaware foes however, using it puts great strain on the user's body.