In Miraculous Ladybug Loveater fanfictions, the characters can be very different from the original. For Ladybug, she may be seen as less in control. The chaos caused by Loveater could make her lose her composure, and she might make mistakes in battles. Chat Noir could be more aggressive in his pursuit of Ladybug's heart. He might be more forward with his feelings, thinking that the dangerous situation calls for him to be more honest about his love for her. Also, other side characters might be given more depth. For instance, Alya could be more involved in the superhero plot, using her skills as a journalist to uncover secrets related to the Loveater situation.
Writers often portray the characters in unique ways in Loveater fanfictions. Marinette, as Ladybug, could be more emotional. The stress of dealing with Loveater might make her more likely to let her feelings for Adrien (Chat Noir) show in ways she normally wouldn't. Chat Noir, on the other hand, could be portrayed as more brooding. He might be more focused on the mystery behind the akuma and less on his usual flirty self.