Lucian showed ND Lulu as a means of sleeping together one night. He really wanted ND to give into the sensual charms of Lulu, but ND was actually incredibly turned off by the quiet sensitive boy he knew becoming a pushy, aggressive mistress, complete with his mom’s magical whip. ND doesn’t mind when he used to pleasure Rin, but he likes Lucian for who HE is, not for who his MOTHER is.
The two ended up doing nothing but talking and sharing candy all night in a slumber party instead. Lucian was originally glum because he didn’t get to show off his other side to ND. But ND wasn’t particularly interested in Lulu in the first place.