The Five Star Stories
The Five Star Stories is one of the longest continuously running giant robot stories of all time, appearing in Newtype magazine since 1986. It's the creation of Mamoru Nagano, a paranoid savant who's only interests appear to be giant robots, ladies' fashion, and exerting total control over his intellectual property. He's made a movie called Gothicmade, and maybe we'll get to see it once he finishes inventing a video codec and streaming service that he considers secure enough.
FSS is set in the Joker cluster, a collection of four inhabited star systems in close proximity, with a fifth system on an elliptical orbit around the cluster that returns every ~1500 years. There are multiple human nations in the Joker cluster, although focus is on the Amaterasu Kingdom Demesnes (AKD). The AKD is ruled by Emperor Amaterasu no Mikado, a godlike being possessing immense powers but taking the form of an effeminate young man. Amaterasu is not fond of formality and normally lives the alter-ego of his given name, Ladios Sopp. Sopp is a meister, one of the few engineers with the skills to create the giant fighting robots known as mortarheads; most of the AKD's strongest fighters use mortarheads designed by him.
Mortarheads are not mere giant robots; despite their size they combine both mechanical and organic components and require an extremely sophisticated control system. These control systems are known as fatimas. A fatima is an engineered life form designed to interface directly with a mortarhead and control its movements. The simplest, mass produced fatimas are little more than a nervous system and are built directly into the mortarhead they are to control. However these are not as effective as their more advanced relative, the bioandroid type fatima. These resemble humans, but they've been engineered to such a degree that they cannot reasonably be called human. Due to the enormous cost and complexity involved in creating them, they are engineered to be potent combatants but also completely servile to their assigned master; the damage a fatima could do with a mortarhead is too great to risk them going rogue.
Mortarhead operators are known as "headliners", and this is the part where FSS gets weird. Headliners are stupid powerful and a good many of them are also kill-crazed psychotic aristocrats. Think of all the character flaws of all your favorite primarchs and then imagine a world where there's hundreds of them roaming around and they all have personal titans.
Presently there are none. At least official ones anyway. Nagano is just too paranoid to license FSS to anyone, and would never stoop to using someone else's game system. Which is really unfortunate because this is a setting that resembles what you'd get if you crossed the Imperial Knights with JoJo's Bizarre Adventure.