Yasu Nagasena was a Human agent of Malcador the Sigilite during the Horus Heresy. An expert tracker and hunter who had served aboard the League of Black Ships, Nagasena was said to be the last descendant of an ancient order of Terran warriors. He was first dispatched with Imperial Army soldiers and Custodes to apprehend the Crusader Host on Terra after the events of Isstvan V.
Afterwards, Nagasena was dispatched to chase down and assassinate Severian, the lone survivor of the Outcast Dead. The two came to blows, but were stopped by Malcador who instead chose Severian to become a member of the Knights-Errant.
Yasu Nagasena was later part of a force sent by Malcador to Nikaea in an attempt to retrieve a Shard of Magnus. Accompanied by Space Wolves and Dio Promus, Nagasena came to blows with the entourage of Ahriman, which had the same objective. Nagasena engaged in a fierce duel with Lucius, his mortal frame unable to best the Space Marine. He nonetheless survived the duel and the battle against Ahriman's cabal.