Luci loses her step for a moment because what Xanxus says comes as a complete surprise. Mafia? Since when was Xanxus in the mafia?

"I knew your family was fancy, but damn, that's a truth-bomb," she says with a laugh that indicates she's trying to recover from this reveal. Not to mention she's relying on Xanxus for the next few steps to make sure she doesn't trip over herself.