To spawn the Urutan Exile, the player needs to kill at least 100 Urutan-Yensa while in Ogir-Yensa Sandsea. The Urutan Exile then spawns in Ogir-Yensa Sandsea/Platform 2 - Refinery atop the main building. The player does not have to chain 100 Urutan-Yensa, just kill them. Killing 100 Urutan-Yensa does not guarantee that the Urutan Exile will appear, however, as like with many rare game, there is a certain percent chance for its spawn.
The Urutan Exile has a low chance to drop the Osafune, a powerful weapon when the player first crosses the Sandsea, so chaining the Urutan-Yensa to increase the chances of acquiring the katana is still highly advised.