The Ke'tsai Sept is a distant, isolated Tau frontier sept that was colonised during the first phases of the Third Sphere expansion as an outpost world, initially stationed with little more than one hundred to a thousand Tau militants at any one time.
In response to Nicassar psychic detection of an approaching tendril of Hive Fleet Erebus, the world was hastily fortified with aid of neighbouring Tau forces in an attempt to dissipate, divert, or at the very least slow down the tyranid onslaught. Drafted forces included D'yanoi, Ka'tsu (notably its last conflict before being permanently quarantined from the Tau Empire), and Gai'kal.
Initially, reinforcement calls demanded the more well-equipped Tash'var Sept to aid in the defence, however the message was almost immediately redirected to the neighbouring Gai'kal due to an alleged "priority conflict" with a local Ork Waaagh! on local mining worlds, which threatened battlesuit production. The redirection of orders without any notice whatsoever sparked a diplomatic incident between water caste ambassadors and diplomats of the Tash'var and Ke'tsai septs, with Gai'kal's almost shocking diplomatic history and persistent rumours questioning the legitimacy of its loyalty to the Greater Good being thrown in the air and used as attempted leverage in an attempt to request Ethereal caste veto powers against Tash'var's decision. However, all Ethereal contact was met with swift denial, with Gai'kal's experience in fighting the Y'he numerous times throughout its history overriding these tensions. When it came time to process the associated documents diverting the order of reinforcement during the last of these diplomatic meetings, the issue was quite blatantly concluded by the chief organising Water Caste ambassador, Por'O Ke'tsai Anya'ko, as "stupid, petty conflicts in the way of direly important matters". As compensation for their supposed lack of commitment, Tash'var granted the "noticeably tense" Water Caste ambassadors of Ke'tsai a set of three XV8 Battlesuits, mantles of which were forbidden to all Tau except fire caste Shas'ui and above, as a crude reminder of what caste and functional positions they belonged to.