The Murakumo (むらくも Murakumo) is a clan from the Dragon Empire nation. They are the Dragon Empire's black ops agency. They make use of hit-and-run tactics such as superior calling from the deck/hand and returning to the deck/hand at the end of the turn. Basically, it is actually very defense orientated in a sense that it is very conserving in terms of hand cards.
Cards like Covert Demonic Dragon, Mandala Lord and Fantasy Petal Storm, Shirayuki maximize the usage of hand cards to exercise a balance of attack while being able to guard effectively. In the manga, Murakumo units are actually part of Nubatama clan.