Shuubi no Kyojin is not an actual character from the series Shingeki no Kyojin (Attack on Titan). The phrase itself means 'Shuubi of the Titans' or could be interpreted as 'Defensive Titan,' but there is no character by this name in the official storyline. In the context of the series, the story revolves around humanity’s struggle against giant humanoid creatures called Titans. However, Shuubi no Kyojin is not recognized among the cast, and thus plays no role in the narrative.