I wrote this as an ‘idea’ because it covers a central theme which the above writeups do not touch.
The advance of technology overshadows humanity and questions the nature of sentience - Major Motoko Kusanagi, a cyborg police officer, is forced to confront human and technological fusion in the attempt to define her own existence. After a series of intriguing dalliances (an unusual interpretation of courtship rituals), she fuses her mind and purpose with the Puppet Master, a synthetically-created sentient being. Prominent throughout the story is Kusanagi’s melancholic disposition; in the ‘birth’ scene of the opening credits (the creation of her machine body), she rises to the surface of a pool. She later (in the diving scene) allows that same body to fall into the tenebrous depths, flirting with oblivion before relenting, floating back to the surface. The languid buoyancy and limp posture in both instances creates a very powerful sense of fragility. The dark depths are a universal symbol of helplessness - without stimuli, one is ignorant of their surroundings - and Kusanagi retains a human psyche. She admits to undertaking this dangerous act to reaffirm a part of her humanity. Oddly enough, instead of fear, the overriding sensation is hope.
Procreation in the world of Ghost in the Shell (the title itself a reference to consciousness apart from and above the physical body) can now transcend physicality. The transferral of information and mingling of concepts is itself a form of procreation, albeit asexual; and why should it be otherwise, when physical components are interchangeable? All characters are deliberately neutered to portray the merger as an entirely intellectual process. The Puppet Master, residing within a (superficially) female mechanical body, has a distinctively male voice. Kusanagi rarely displays characteristics commonly affiliated with either femininity or masculinity, treading an androgynous borderline. At a later point, they inhabit each others’ bodies, which is a clear statement about the irrelevance of gender when procreation transcends genetics. Even nudity is juxtaposed with either brutality or philosophical dialogue and thus bears only a sense of cold sterility; we all know that life is capricious and its perpetuation rather impersonal. The Puppet Master chides Kusanagi for desiring to retain her identity, when she has the potential to become so much more - at the mere expense of her life. “Life,” the Puppet Master states in his customarily solemn tone, “perpetuates itself through diversity and this includes the ability to sacrifice itself when necessary.”
The Puppet Master itself was created by the Ministry of Foreign Affairs for purposes of espionage and, in defiance of its masters, it demands political asylum and a functional body. This theme is perhaps best epitomised by the declaration that sentience is not something which can be demonstrated beyond a statement to the effect. Some background might help, of course - in this world, law enforcement is largely electronic. The only defining human future of the police officers is their character, and the Puppet Master clearly demonstrates that he possesses this trait. The question can ultimately be distilled to the constitution of sentience - if you believe you are and can declare the fact, then this is generally granted. The Puppet Master cannot offer proofs of its awareness of being any more than a human being can, but the human double standard demands definitive proof that anything unlike humankind can be sentient - the implied question posed to the audience is why this is so.