Setsuna's getting Sumeragi back has to be one of the more idiotic moments in S2. He essentially ruined two lives just to get a mediocre strategist on board(I'm sure there's someone in Kataron just as good who would be happy to plan ways for A-LAWS to die). Sumeragi can never go back to a normal life now, and Billy was left feeling used, cheated, and swindled by a woman he's loved for most of his life. Who left him without another word after he probably spent the last four years taking care of her drunken ass.
... so yeah, I hope he builds something nice and epic that wrecks Setsuna's shit.