Boys and Girls (男の子女の子編 Otokonoko on'nanoko hen) is the fourth Black Lagoon omake. It was originally released in the fourth manga volume on July 19, 2005, and it was later animated and released on the fourth Japanese Blu-ray disk on February 10, 2010.

Waking up with a headache from a hangover, Rock enters the bathroom and suddenly notices that "he" is now a woman with large breasts. Yelling in shock, she runs to the Lagoon Company office as her breasts cartoonishly bounce up and down, shouting in dissatisfaction to her fellow pirates that she has turned into a woman with huge breasts. When Rock enters the office, Dutch and Benny, who are also women and dressed in different clothing, ask her what is wrong. Rock becomes speechless at their gender change, prompting Benny to ask her why she is panicking and if she is still hungover. Nearby, Dutch notices the manly Balalaika, who asks Rock why she is so excited. Seeing Rock cry and run away upon further disbelief, Balalaika remarks that she is a strange woman. While running, Rock runs into Chang, who is a woman and nonchalantly greets the pirate as if there was no change in everyone's gender. Likewise, the manly cowboy Eda greets Rock and compliments the latter's breasts. Hänsel and Gretel claim to respectively be a girl and boy, but Rock sees no difference due to their outfits and wigs also switching.

When Rock thinks that she cannot handle anymore, Revy greets her. Hugging the gunslinger, Rock expresses relief that Revy is still a woman. Laughing, Revy retorts that Rock is crazy and states that he is actually a man. Immediately, Revy pulls down his pants to show his genitals to Rock, shocking her completely. Elsewhere, the butler Roberta, a man, claims to the young Garcia Lovelace, a girl, that he has heard a woman scream. Unconcerned, Garcia tells him that he is hearing things. Overwhelmed by the encounters, Rock mutters through tears that there is nothing else to see.