Bunny Girl Universe (バニーガール ユニバース編 Banī gāru yunibāsu hen) is the twelfth Black Lagoon omake. It was originally released in the thirteenth manga volume on December 19, 2023.

Wearing a Playboy Bunny uniform with her VDV coat around her shoulders, Balalaika declares to everyone that they are in the bunny girl universe. She elaborates that she will transform everyone into a bunny girl, confusing Revy and Le Majeur. Firmly speaking, Balalaika retorts that everyone in the world likes bunny girls. Sitting to the side and drinking some tea, a relaxed Yukio Washimine remarks that it is certainly rough for everyone, but not for "retired" characters like herself and Hänsel and Gretel. Having forgotten to mention it, Balalaika clarifies that retirees also qualify for the event, causing all three to spit out their drinks in shock. Starting the transformation, various women, including Revy, Eda, Shenhua and Sawyer, appear with Playboy Bunny outfits on, causing great embarrassment. Likewise, the retired characters, such as Roberta, Fabiola, Yukio and Maki, are also given revealing Playboy Bunny outfits, shocking them as well.

Transforming the twins into bunny girls, Balalaika claims that she is getting excited and wants to go all out, also transforming Jane and Feng Yifei into bunny girls. Asserting that round two will begin, Balalaika embarrasses Le Majeur by turning her into a bunny girl, then turning the four other women of Les Cinq Doigts into bunny girls, confusing them. Outraged at the humiliation, Rock asks Balalaika to stop it since the clothing is outrageous for the women. Benny and Chang agree, adding that as male characters, they have to put a stop to the madness. Happily informing them that being a man will not spare them, Balalaika turns the three men into bunny girls. Whereas Rock and Benny are completely embarrassed, Chang nonchalantly accepts his new reality. Stating that he will not allow it, Dutch asserts that there is no demand for male bunnies, and Benny and Rock cover their chests. Replying that she sees his point, Balalaika decides that she will give him a special reverse bunny uniform. Suddenly, Dutch screams as Balalaika gives him a reverse bunny suit, also receiving heart-shaped pasties.