HARUKO HARUHARA SPOILER!
Haruko presents herself as connected to the Galactic Space Patrol Brotherhood, but the original OVA gives Naota very good reasons not to take anything she says at face value. Her real obsession is Atomsk, the Pirate King whose power she wants for herself. Naota matters to her because his N.O. channel gives her a way to reach him.
That does not make every interaction between Haruko and Naota fake. FLCL deliberately makes her harder to sort than that. She manipulates him, endangers him and plays with his feelings, but she also becomes attached enough that their final separation is not emotionally empty.
Haruko is funny because she refuses normal boundaries. She is dangerous for exactly the same reason. Whatever role she claims to be playing, she ultimately follows Atomsk.
HARUKO THROUGH THE ARCHIVE //
ATOMSK & MEDICAL MECHANICA //
Open page →Naota Is the Route · Atomsk Is the Target
It is not.
What she actually wants is Atomsk. Naota matters because his N.O. ability gives her an unusually powerful route through which objects, Medical Mechanica machines and eventually Atomsk himself can cross into Mabase.
That makes Haruko's relationship with Naota uncomfortable by design. She enjoys him, provokes him and becomes part of his life, but she is also using his body and his feelings to pursue something she wanted before she ever met him.
GUITAR & ORDNANCE //
Open page →Haruko's Rickenbacker 4001
Open →Midnight Blue · Instrument, Weapon, Tool
She plays it like an instrument when FLCL feels like being a music show and swings it like a weapon when FLCL feels like being an action show. It also carries impossible modifications, including the pull-starter mechanism she uses repeatedly.
The bass is involved from the moment Naota's first forehead growth appears and remains part of Haruko's attempts to force open the route to Atomsk.
GROWING UP IN MABASE //
Open page →Attraction, Manipulation and the Person He Cannot Control
She is exciting, invasive, funny, dangerous and completely unwilling to behave according to the rules Naota uses to keep the rest of his life manageable. He distrusts her and wants her attention at the same time.
Haruko has her own reason to stay close. Naota's N.O. ability makes him useful in her pursuit of Atomsk, and she repeatedly pushes him toward situations he does not understand because she wants access to what can come through him.
The relationship therefore never becomes a clean romance or a clean manipulation.
Episode 6 · He Gets the Power She Wanted
Atomsk manifests through Naota, placing the enormous power Haruko has been chasing in the hands of the boy she treated as the route to it.
Naota confronts Haruko carrying that power, tells her that he loves her and then releases Atomsk instead of surrendering him to her. Haruko immediately chooses the chase and follows Atomsk away from Earth.
N.O. CHANNEL MECHANICS //
Open page →Amarao provides explanations for N.O., but FLCL never turns them into a complete set of measurable rules. The safest way to understand the phenomenon is by watching what it does.
Haruko Tests Kamon
Open →A Possible Route That Goes Nowhere
He cannot.
The result is bizarre even by Nandaba-house standards, but the important part is what Haruko learns: Kamon is not capable of giving her what Naota can.
Robots emerge through him. Weapons emerge through him. Canti repeatedly absorbs him and draws on much greater power. Eventually Naota becomes the point through which Atomsk himself can manifest.
Why Haruko Hits Naota with the Bass
Open →The First Blow Opens the Problem
Later events make clear that Haruko is deliberately interested in Naota's N.O. potential and repeatedly uses her guitar around the openings that appear through him.
The OVA does not give us enough to describe the first strike as precise neurological surgery or the installation of a permanent device.