Assuming the player is not the Last Dragonborn (via another mod):
A truce happens during the Skyrim civil war, reportedly orchestrated by a Dragonborn hero to facilitate dragon capture. This Dragonborn rode the captured dragon, disappeared, and hasn't been seen since. In the wake of their absence, hostilities resume.
The player character encounters the Spirit of the Time Wound, who insists that the Dragonborn is caught in Time Stasis. According to the Spirit, only the player character can assist.
Should the player agree, they will explore the ghost giants of the Jerall mountains and storm Skuldafn alongside them, ultimately aiding the Dragonborn in Sovngarde.
As a reward, the player character gains a power to toggle to Dragonborn mechanics, for the convenience of use of shouts, dragon souls, and the execution of the Dragonborn DLC or quest mods that require shouts.
Assuming the player is the Last Dragonborn
During the Alduin's Bane scene, player control isn't locked for an extended period. The Spirit of the Time Wound appears, requesting the player's assistance in its repair. Jills, time-repairing dragon entities, used to perform this task and still do, albeit less visibly, likely a repercussion of the ancient Dragon War.
The interior of the Time Wound is a basic maze, each chamber representing a time segment of the Alduin's Bane scene. Access to these chambers is locked, and doors within the Time Wound consume one passkey each. The Spirit possesses one such key initially and can forge additional from the ancient dragon priest masks. The Time Wound itself provides hints at the locations of dragon priest masks, in a manner reminiscent of the Dawnguard DLC.
While the maze is randomized, the fragment of Alduin's Bane scene that unlocks the Dragonrend shout is in a chamber just one door away.
Other chambers may provide clues on how to evade Time Stasis in Sovngarde.
Both variants serve to delve into the canonical and fan interpretations of Hero/Prisoner lore within the Elder Scrolls.
Like the 3D civil war storyline, this is an outline for what occurs if the new narrative is activated after the main Skyrim quest is completed.
A courier mistakenly delivers a package to the player character, intended for someone else. After locating the intended recipient and delivering the package, it's revealed that the recipient is a ghost possessing unique shapeshifting powers. Upon hearing the tale of a successful hunt, the ghost gains the ability to temporarily transform into a specter of the hunted game animal.
If the player character is the Dragonborn, they can recount their dragon hunting experiences, including their victory over Alduin. If the player doesn't share this, the ghost will soon hear the tale from a wandering bard.
It remains ambiguous whether the resulting specter of Alduin is genuine or an imitation.
Surviving the ensuing debate rewards the player with the ability to freely manipulate the parameters of the 3D Civil War.
This is meant to delve into the dichotomy of Alduin and Akatosh and related lore.
In future versions, early branching into this narrative is being considered, particularly if the player is not the Dragonborn. Encountering the specter before dragons appear shows off its shapeshifting abilities for wild beasts. Certain characters, aware of both the specter and the Dragon Prophecy, foresaw the events and devised a plan to exploit them, but they underestimated the specter's potential.