Both the wills of individuals and the collective will of humanity can usually be likened to a swarm of bugs around a light; moving chaotically without coordination. But a majority of the bugs that comprise Nagi’s will are aligned towards a a confrontation with the serial killer, for which she is diligently preparing but may still be woefully overmatched.
That certainly seems to be Sasaki’s opinion on the matter, as the bug within him can’t simply let her be, lest she end up hurt or killed simply for following her own will and sense of justice. If anyone is going to protect her, he figures it should be the one who deprived her of her father, the person who would otherwise be responsible.
Sasaki’s supicions are confirmed: Kisugi has set a trap for Nagi, whom she suspected would show up in superhero guise (Nagi’s jumpsuit is indeed totally badass): have her tranquilized via sniper rifle, then proceed to explore her delicious fear.
Sasaki delivers a killing blow before he notices it isn’t Kisugi, but Pigeon, who stabs him right back as revenge for killing Kuroda (her own bug she couldn’t ignore). But Pigeon distracts Sasaki from Kisugi, who puts her arm through his chest.
Just like that, the backup both Sasaski and I believed would be crucial to Nagi’s survival has been taken off the board in gruesome fashion, a sentiment reinforced when Sasaki tosses his corpse out the window, then leaps out herself and lands on her feet far too close to Nagi for comfort.
But true to her name, Nagi keeps calm and carries on. She starts to flee Kisugi, first on foot then on bike, but the Kisugi’s personal flirtation with evolution has made her as fast in heels as Nagi can pedal, and it isn’t long before she’s caught her up.
Yet still, there’s something about the deliberate manner in which Nagi flees—constantly looking back to make sure she’s being followed—that suggests the chase is unfolding precisely how Nagi planned. Even when Kisugi loses her temper and starts dunking Nagi’s head in a pond and kicking the shit out of her, there isn’t a trace of panic on Nagi’s face.
Kisugi finally visualizes Nagi’s weakness—someone she loves dying before her, like her father—while her actions confirm to Nagi that she’s someone who preys on those perceived to be fearless. Kisugi is right that no one is truly fearless, which means there’s no one she can’t feed off of.
But Nagi’s fear in that moment is less that she’s about to be killed or worse, but more worry that the intricate plan she’s set up might fail. That she will fail to become the superhero she thought she could be. But it doesn’t fail, because Kisugi is part of the circuit of the pond, while Nagi in her thick insulated suit isn’t…and has a weapon that shoots electrical arcs.
Thus Nagi does the equivalent of drop a giant plugged-in toaster into the bathtub, zapping Kisugi with thousands of volts and doing significant damage to a body already taxed to the brink by all of her DIY “evolution.” When Nagi puts her in an arm hold, the arm pops off, and Kisugi flees.
It’s then when an ally far more powerful than Sasaki appears, only to voice their surprise Nagi didn’t need them after all. The situation was always under control, though Nagi could rightly say she relied on some luck in everything going perfectly.
Now Kisugi is the hunted, and full of fear. Turns out she’s a fear ghoul, and definitely an enemy of humanity, which means Boogiepop has popped up to finish her off. But they give credit to Nagi for defeating Kisugi and making the kill so easy.
Nagi manages to be with Sasaki before he dies, and his last words are of relief that she’s still alive, and that “the bug” within him isn’t so bad. Boogiepop then determines it would be best if the blame for the serial murders were placed on Sasaki, due to the complications of the culprit being a doctor of Kisugi’s caliber.
More than that, the bug in Sasaki would be fine doing whatever Nagi wanted, including piling the blame on him. Nagi, meanwhile, still feels like she messed everything up in the case. But she learned a lot from it too, and that wisdom gained will serve her as she keeps fighting. Not to mention “Boogiepop”, as they introduce themselves to Nagi, will be there to help when needed.
Back on the ruined world, which we learn isn’t the Earth of Nagi or Touka but some kind of “distorted world”, Boogiepop wrap up their story to Echoes, as the two contemplate the causality starting with Kuroda saving Nagi, all the way to Echoes and Manticore showing up on Earth.
Echoes muses that Nagi continues to fight because she’s “carrying on the feelings of those she encounters.” That’s one way you could describe an investigator, or a superhero, or both, which is what Nagi is. As Echoes takes his leave, Boogiepop commits themselves to leaving the distorted world and returning to Earth.
Because even if Boogiepop doesn’t know precisely how or why they pop up, they understand intrinsically that it is right for them to do so; that it’s beneficial to humanity and thus necessary to continue. Even Boogiepop has a bug.