After the alleged betrayal of Commander Farsight, Aun'Va selected a more-steadfast replacement to conduct the Third Sphere Expansion. The great Ethereal selected Commander Shadowsun, also known as O'Shaserra, for this role. O'Shaserra was already a well known and respected warrior, having earned her command in the deserts and jungles of the K'resh Expansion, where the Greenskin menace in that sector was finally contained. Against the Tyranids, she led several devastating raids that disrupted the alien command and control structure so thoroughly that the Tau armada was able to scatter and destroy an entire splinter fleet without the loss of a single vessel.

Under O'Shaserra's inspired leadership, the Tau Empire expanded significantly into its Third Sphere. With Imperial attention elsewhere, and the local Tyranid and Ork menace temporarily contained, Tau settlement colonies and pioneer teams reached far and wide into the outlying systems of the Damocles Gulf, the Perdus Rift, and much farther afield. Although the encroachment on Imperial space was relatively minor, the Tau established no fewer than five Third Phase colony systems in a halo around their existing sept worlds. With Commander Shadowsun at the head of their armies, the shadow of O'Shovah seems to have finally been laid to rest, though his exact whereabouts still remain a mystery.

Commander Shadowsun is a Special Character. She may be used in Tau armies of at least 1,500 points as an HQ choice.