|“||Ah, Pops--you've tormented me a lot...||”|
–Number 3, plainly stating her case
At the time, not much remained unknown about vectors, the Diclonius Virus and the Diclonius themselves. A young diclonius, only known as Number 3, escaped from her containment unit after hiding how her vectors had grown in the recent months. During her escape, she killed at least three DRI personnel, including a scientist and two security guards, with more possibly killed offscreen. She made her way to the office of Kurama, Oomori, and Professor Kakuzawa, where she infected the former two with the virus, unbeknownst to them, before being shot dead by the latter.
Even many years later, Kurama remembers this battle, as it permanently destroyed his family and marred his life.
At play in this pre-series flashback situation are almost all the elements seen in the present-day of the story, though Kurama himself could not have known this at the time. In particular, the scientific training of the DRI support staff is immediately brought into question since they failed to take precautions around Number 3. Though her powers hadn't shown any recent growth, Number 3 and other Diclonii like her could be very volatile regarding their "caretakers." Her power ceasing to grow didn't mean it never would or could grow again.
Similarly, the possible and perhaps likely disdain of the Kakuzawas for the security staff is perhaps chronologically first demonstrated here by the ineffectiveness of their standard firearms against a Diclonius, a hard fact that would replay again and again until the final moments of the DRI's existence. This disdain for all but their kind shows in even starker relief by the fact that it is Professor Kakuzawa who guns down Number 3 in apparent glee. Not only does he kill someone who is (according to his family's traditions)'one of their own,' but he does so with a weapon unavailable to the vast majority of the staff who face this sort of threat on a daily basis. While both things are quite in character for him and his father, the mask breaks a bit more here, and much earlier than in the main time frame.
Though the story offers clues, it does not directly state why Number 3 sought Kurama out. While she says that she wished to thank him, it remains unclear if she meant this sincerely or sarcastically. It's also possible she meant it as a mix of the two. On the one hand, Kurama was the only researcher shown to object to or be physically disgusted with the experimentation and intervene on Number 3's behalf. On the contrary, she could conceivably have been upset that, while objecting, he did not stop the process entirely or otherwise do more. Her infection of him also falls into question, motive-wise, as it could have been deliberate, an unintended accident resulting from being near him, or the side effect of a failed effort to kill him. If a conscious choice, then the question becomes whether this was to see to it that a future Diclonius had a kind man for a father or punishing him by ensuring he would have a child with her problems, and in Mariko's case, more.
Number 3, of course, ended up posthumously raising and answering crucial questions about the Diclonius, being the means and manner of infection for new births, learned the hard way by Kurama and Oomori, and the existence of an original infecting party.
She was something more, story-wise. She is the start of Kurama's journey into the world of the Diclonius. It is for Number 3 he raises his first objections to the carnage that was these girls' short lives. It is from Number 3's escape that he first realizes that, little girls or no, they can, in fact, present some danger. In the wake of first Oomori's daughter and then Mariko, he becomes something perhaps far colder than his hardened colleagues, killing these children after they have entered the world of the living. Since Number 3's actions cost him Mariko in most respects, the Human feelings he cannot entirely put aside come to rest on Nana.
These factors may well render Number 3's escape as the most pivotal such moment in the series, falling behind in importance only to the flight that starts the series in the present.
|“||Was it that she saw me as the only Human feeling sorry for her?||”|
–Kurama, starting the first of several long and painful journeys at the passing of Number 3