Do you get it? They are having SEX.....IN THE ROBOTS!
The father dude convinces them if they can't PROCREATE and have SEX (in the robots btw, doggystyle, raw, it's wild) they are nothing!
The wild haired short character, Zorome, is having SEX with his partner for VALIDATION, you wouldn't have guessed that right?
If you watch closely and pay attention, it mentions that the partners need to be compatible to make the robots go good, they need to be compatible to have good SEX!
The quiet, virgin main character Hiro, which, few know this, but his name sounds like the English word, "Hero" which, according to the Merriam Webster dictionary is "a person who is admired or idealized for courage, outstanding achievements, or noble qualities." His noble quality is that he is the only dude who can have good SEX with the WILD, EROTIC, SEXY CHARACTER, 02! If you vacantly watched, you may have missed this!
She has horns, like a DEVIL, or an ONI (Her name in the show is 02, which if you say the numbers in Japanese, sounds like "oh-nee", few people know this!) and she has sex so good that the main character passes out! And she KILLS anyone she has SEX with!
When Ichigo wants to get in the robot with Hiro (Hero in English, remember!), they don't have good SEX because they don't synchronize well! This is an important detail that I have seen many people miss, and it isn't at all touched on in the anime!
Most of this will fly right over the average person's head, as it is very subtle in the anime, as well as the manga, but the more you watch and analyze each moment, it will become more clear to you!