this is a very late reply, but figured i’d sum it up as easily as i can
Yingxing and Dan Feng were part of the high cloud quintet, and ended up committing a grave sin. because of this they faced heavy punishment.
Yingxing became marastruck(basically he slowly turns into a monster) and became immortal, now going by Blade the stellaron hunter. Dan Feng played a part in Yingxing becoming marastruck, which is why blade harbors such resentment towards him.
Dan Feng, was imprisoned in the shackling prison and forced to be reborn as Dan Heng, who doesn’t fully remember his past. He was permanently exiled from the Luofu, and now travels with the astral express
In their past lives Yingxing and Dan Feng were canonically in a relationship prior to their sin.
Side note: Yingxing is also called ren bc that’s the chinese character used for blade
would any kind soul wish to explain the lore (づ￣ ³￣)づ