In the old Astroboy mangas/show, Astroboy gets oil by having some device plugged into his butt. Strange, yet innocent, right? Well, think about it: This is a robot who looks like a nine-year-old boy. He's having a phallic-shaped oil-delivering object being shoved into his butt while EVERY OTHER ROBOT in the mangas/show receives their oil by drinking it from a cup. Of course, it begs to be added that Astroboy is the ONLY robot that pretty much has no clothes on save for some underpants and shoes. The other robots have clothes. And remember: the creator was trying to make a robot replacement for his dead son... Pass the Brain Bleach, please.
In the 2003 anime, Dr. O'Shay speculates that the days Tenma spent with Tobio/Astro were probably the happiest days of his life. So what's the first step in Tenma's Villainous Breakdown? Erasing Astro's memory so he can relive those days.
The 1982 anime features an episode where two robots fall in love due to what O'Shay explains is a strange tendency for robots with similar designs to form strong attractions. Several episodes later Astro gets a love interest in Nuka, a robot based on his prototype blueprint.