My Backer Is an Emperor for the Ages

Reserving this spot for now.

For example, you discover that you've transmigrated to the An Lushan Rebellion, the end of the Song dynasty, or some other chaotic era, and you're doing your best to stay alive. Then you find out that Ying Zheng or Li Shimin has transmigrated into your own father or older brother, and the two of you join forces to rebel as father and daughter, or brother and sister.

Theme: Save a crumbling empire from collapse.