So here is what I came up with:
The Ukri are a people constantly at war. They developed along the western edge of Baltien, but despite ready access to the ocean's vast resources, did not develop sailing techniques for centuries. Forced to eek out a living without being able to fish on a large scale, they eventually rejected small-scale pearl diving and fishing in favor of raiding their wealthier neighbors to the east. They became a very warlike people, and their mythology reflects this.
The Ukri believe that death brings them to the Enki-des, or Soul Gates. The Enki-des is a series of seven gates, and the Ukri spend their lives preparing for the seven trials they must face in order to pass through the Enki-des to reach Furrma, or Paradise.
The first six trials are combative. A deceased Ukri must battle and defeat a powerful guardian to pass through the first Enki-des, then the second, and so on until the last. The final trial is not a trial by combat, however. Instead, the Ukri must present his or her Enko-ori, or essence pearl, to the Enki-Rochimga, roughly translated as Guardian of the Soul, who is usually depicted as a giant white bear standing upright on two legs. If they are able to present their Enko-ori to Enki-Rochimga, the Ukri are permitted into Furrma. Obtaining these Enko-ori is critical to the Ukri--without it, their battles through the first six Enki-Des will be for naught, and Enki-Rochimga will devour them.
There are two ways to obtain one's Enko-ori. It may be obtained in life if one lives a long, honorable life. In such cases, one's Bilchidru, a sort of observing spirit, will grant one his or her Enko-ori immediately after death.
For those who do not live long enough or honorably enough to be granted an Enko-ori freely, there is still hope. They must search the Enki-des for their Enko-ori. This search may take a very long time, and they will be fighting the guardians of the Enki-des the whole time.
Subsequently, the Ukri prepare their entire lives to fight. From the time they can walk, they are told to run. From the time they can lift a stick, they are shown how to use a spear. They are trained to fight, and they do so exceptionally well.
Interestingly, they are not bloodthirsty warriors, like many of the warrior nations that developed in Baltien. This is likely because of their quest to obtain their Enko-ori by living a long and honorable life. While they are willing to fight and raid as a way of life, they do battle as bloodlessly as possible, seeking to leave their opponents alive, but incapacitated.
So, the game concept is pretty straightforward. It's a solitaire game, wherein the player takes on the role of a deceased Ukri warrior, and must battle his or her way through six unique guardians. After defeating a guardian but before advancing to the next stage, the player may search the area for his or her Enko-ori. If he or she does, they must battle the guardian again, regardless of whether or not they are successful in finding their essence pearl. Alternatively, their may be a way to search the area while doing battle, but the player will be distracted and thus take damage from the guardian. I haven't worked out how this might work mechanically, yet.
If the player is able to reach the final gate of the Enki-des and present his or her Enko-ori to Enki-Rochimga, he or she wins. Otherwise, he or she loses.