Wukong and Liu Er as ex partners, their 'mafia empire' having fallen due to the 'Heavenly Court', betrayals and infighting. At the end, each thing the other died an somehow continue with their lives, Wukong even ending up working for the Heavenly Court.
Years later they somehow reunite, and after some time they kind of make up (Liu Er is out of a home and a job so he ends up moving in with Wukong and becoming his partner again)
And then a kid shows up at their door, thinking Wukong is his dad (no-one is amused), they don't know what to do with the boy, they don't really have friends (Ne Zha is a friend but it's also even more involved in their business than them since him -and Ao Bing cuz ofc I'm mixing that in- is who investigates everything and gives them their missions) they think about just leaving the boy but they don't really have the heart go do that (also is not like the kid can't come back and even being some unwanted attention with him)
So now they're taking care of the kid, Xiaotian, MK (later they will learn that Wukong isn't actually the dad, but older half-brother because same sperm donor)
Also, Tang and Pigsy work at the kindergarten MK attends, Tang is his teacher and Pigsy is the school's cook. MK, Mei and RedSon are classmates
If deltaswap is where they change personalities/roles, then it's safe to assume that SwapRune is where Kris is the only monster in a human town. Or should be InvertedRune? DeltaInverted?
Just like Kris used to wear the horns to be more monster-like, this Kris paints their hair brown to seem more human-like.