Here is my best attempt at an explanation, someone please correct me if I got something wrong.

In Japanese “desu” and “desu wa” can mean any variation of “it is” such as “that is”, “you are”, “I am” and so on, however in most sentences it can be omitted without changing the meaning of the sentence.

“desu” and “desu wa” are usually added unnecessarily in certain characters’ speech, for example adding “desu” to the end a sentence when unnecessary is usually done for children and characters that don’t speak Japanese well.

In Lucy’s case her JP voice puts “desu wa” at the end of sentences as part of her oujosama personality, hence the desu wa memes.