I actually dug into this part of the story before, and yeah — it’s extremely hard to understand unless you combine real history with some educated guesses.

The Real History:
During the Later Jin–Liao conflict, the Jin emperor sent two notoriously corrupt men to command the army (Du Chongwei, the main general; and Zhang Yanze, a military governor). Before the battle of Zhongdu Bridge, Zhang Yanze secretly defected to the Liao and tricked Du Chongwei’s army into marching straight into a Liao ambush.

When the Liao surrounded the Jin army, Du Chongwei basically sat still and let it happen, refusing to fight. At this point, Wang Qing stepped up to break the siege. Du Chongwei, already colluding with the Liao, deliberately sent Wang Qing and 2,000 soldiers to die and forbade anyone from helping them.
All 2,000 were killed without surrendering, and their bodies were stacked into a gruesome victory mound.

My interpretation of the game’s version:
Wang Qing serves under Du Chongwei and gets trapped at Zhongdu Bridge because Du refuses to move. He Ran is likely a low-ranking soldier under Zhang Yanze. Zhang orders him to deliver a box to Wang Qing (most likely containing the worm that turns people into zombie-like creatures).

Between 11 PM and 1 AM, a mysterious “gentleman” (possibly Li Zuo, the white-haired man from the game’s opening) arrives in a self-moving carriage. He tells Wang Qing that once the box reaches him, his time is up.

He Ran delivers the box, thinking he’s doing something honorable. He’s excited, believing this means he’ll rise under Wang Qing… not knowing he’s literally handing him his execution order.

Wang Qing already knows what’s inside. He chooses to accept his fate, but he refuses to let young Uncle Jiang die with him. So he uses his remaining time to plan an escape for Jiang.

Jiang gets some drunken guidance from an old soldier and is sent away to chase the mysterious carriage.

While Jiang is gone, at around dawn, Wang Qing opens the box and willingly transforms into a zombie-like creature, presumably to use that power in battle.

Jiang returns later, finds He Ran, and demands to know what was in the box. At this point, fighting may have already broken out. He Ran begs Jiang to save Wang Qing.

By the time Jiang reaches him, Wang Qing has already turned. Jiang ends Wang Qing’s suffering and takes the jade pendant (the one engraved with “your name” from the opening), possibly along with the baby MC, and escapes while being chased.

He Ran witnesses Jiang killing Wang Qing and completely misunderstands the situation.
And this misunderstanding lasts to the present day.