Shien translated means "Blue flame". Shōgun is a military rank and historical title in Japan.
The Shien card series was most likely inspired by the great Japanese warlord Oda Nobunaga. He shares almost all of the traits that are popularly associated with Nobunaga and looks exactly like the "Samurai Warriors" depiction of Nobunaga.
Each new iteration of Shien, except "Tenkabito", has 1000 less defense than the original, with "Great Shogun" having 2400 DEF, "Shi En" having 1400 DEF, and "Shadow of the Six Samurai - Shien" having 400 DEF.