Curate, connect, and discover
So the premise of the whole au is that WWX is tired of people insinuating that the only reason he has as many privileges he does in his life is because he is JFM's bastard son.
Since JFM hasn't stopped the rumors its A) making seem very likely that it's true and B) making YZY insanely pissed.
Fast forward to the CR Era WWX and the other Jiangs get pretty on edge anytime someone brings his parentage since that particular conversation topic leads to nothing good.
One day when somebody finally asks WWX about it he decides enough is enough, that he is tired of letting random people make assumptions about his parents, how it's staring to strain his relationships with his siblings, how YZYs rage is steadily increasing towards everyone and how the one person who could end the whole thing refuses to ever say anything.
So in between his detentions with LWJ he begins to research different identification spells and relics in hopes of finding one that could reveal parentages or bloodlines but can't find anything (which they probably have in canon but shhhh we need the story to happen) but he is left several ideas running around his minds and gets to work.
Fast forward through many experiments, one expulsion, and many more months WWX has made the world's first DNA test. It's a tailsman that will either glow when it recognizes a blood realtion between users or crumble to ash if there is no blood tying them together. Despite spending several months making this tailsman WWX hasn't found a good opportunity to bring the subject up to JFM so he slowly starts to believe that he won't get a chance to use it use it.
But fortunately for him Lotus Peir is hosting the next the Discussion Conference and you know some shit will eventually go down. Let's just say that after most the events are down JGS says some shit like "oh how generous and brave of you to make your bastard your head disciple despite the backlash, how do you and your wife deal with it??". And you can instantly feel all the rage and tension coming from everyone room but then WWX realizes that this is a great (not great but beggars can't be choosers) opportunity to use his invention and prove that his parents are his parents, opens his mouth and says "Sect Leader Jiang is not my father and I can prove it right now if yall let me".
So after he explains himself (despite the death glares from YZY, the greedy looks from JGS and someone in the back who keeps grumbling how this ridiculous and borderline unorthodox) and provides actual proof from two willing volunteers that his tailsman is safe and that it works he finally gets to test himself and JFM and proves once and for all that all those rumors were bullshit CSSR had never cheated on her husband.
Of course some in the audience are still more interested in stirring shit up instead of keeping their mouth shut and try to imply that since his station isn't as high as the real heirs they shouldn't trust his word. And JC who has been shockingly quiet during this whole ordeal finally snaps and goes "if you refuse to believe that his invention works despite having proof before they went maybe I should go and get tested right now so you can stfu!!"
But YZY freaks the fuck out when he says this and starts going on about how he has nothing to prove, that she forbids him to take the test and everyone in the room are now just kinda side eyeing each other and her because why would she not allow her sects heir to take this test? Unless...
Somehow JFM gets JC to take the test, despite YZYs vocal protests, and the tailsman paper crumbles between them.
The room goes dead silent before WWX offers up a flimsy excuse that the tailsman may have made an error, but it's too late now. Everyone knows that the tailsman works and now they know JFM is not JC father.
That Lotus Pier's heir is a lie.
Nobody asked but for the last several days I've been thinking of an au where in the Cloud Rescess Era (or adjacent timeline) WWX invents like the first DNA test and through a series of events reveals that JFG is not JC's father.