Just read the latest chapters. And I thought the same thing, Ao might have died and that's where the lil bro enters. He might have left Xun in his care. But who knows, since this is already dropped, then lets just leave it to our imagination I hope the author finish this in the future tho.
WHAT IF XUN IS TRYNNA BE A CARDIOLOGIST BECAUSE AO’S HEART CONDITION KILLED HIM