Apparently, it's in omakes. I only know it because of the Arcobaleno arc so I'm not one to talk either. Luce is the Sky Arcobaleno, batchmates with Reborn. The kid she was carrying was Aria, who kinda... died, idk? in the TYL arc. And then there was Uni, who Gamma has the pedo-hots for. orz

Confusing shiz.