The Boys Next Door was an all-male organization resistance similar to the Kids Next Door existing in an alternate dystopian future seen in Operation: F.U.T.U.R.E.. They fight against Madame Margaret and her Girl Squad, who had taken over the world and turned almost everyone into girls. The Boys Next Door are a ragtag group and use very basic and improvised materials and sports equipment for clothing. They often wear head and ears bands, shoulder pads, and ropes tied around their bodies. They all wear jetpacks during battle.
In Operation: F.U.T.U.R.E., 75 years later following Numbuh 4's defeat at the hands of Margie, they were founded and led by an aged Numbuh 4 in order to overthrow Madam Margaret from the power. The resistance included boys resembling (and presumably descendants of) Numbuhs 1, 2, and 5. While planning an strike against Margaret's Girl Squad after saving a little boy from three Girl Squad operatives, Sally Sanban, Numbuh 3's granddaughter, joined the BND disguised as a boy and after being discovered shortly before their final battle convinced them to let her stay to keep her safe from Madam Margaret; her joining prompted Numbuh 4 to rechristen the group the Kids Next Door. Numbuh 1's apparent descendant apparently developed crush on Kuki's granddaughter, as they are seen acting shy around each other and blushing when they talk to each other. During that time, Numbuh 2's apparent descendant altered as Girlifying Rifle into a Boyifying Rifle.
As Margaret located them with a locator that Sally was inadvertently wearing, the Boys Next Door began their final battle against the Girl Squad. At first, they managed to transform two girls into boys, but when Madam Margaret activated the Supergirlifier Cannon, all the BND operatives, including their leader, were transformed into girls (although it could have been probably that some managed to escape as they were on their secret hangar). However, their sacrifice helped Numbuh 4 to save many lives, as he used Madam Margaret's time machine to go back to the past and defeat Margie during their first encounter, erasing her alternate dystopian future.
- It's completely unknown how the Boys Next Door's existence was affected due Margie's defeat in the past, but it seem that the division was erased from existence as it would not be necessary to created a all-boys resistance as Madam Margaret would not be able to create the Girl Squad as she would be captive at the Kids Next Door Arctic Base. Whether this altered their members' lineages or avoided their births is completely unknown.