Number 28's role in the story is heartbreakingly tragic. After being brutally and repeatedly raped by The Unknown Man, she was eviscerated and placed within a case, used as a sensor for other Diclonii. Further, researchers implanted with a device designed to cause her excruciating pain just in case her vectors should emerge. She also had her vocal cords severed so she could not even cry out in pain. The Unknown Man intended to use her to track other Diclonii, especially Lucy, but instead, she found Nana at the Maple House. She contacted telepathically, appearing in the form of a faceless, legless monster, warning Nana of the Unknown Man and begging her to kill her to end her suffering. In this condition, even with life support, she would not have lasted more than three days. When he discovered Number 28 had found Nana instead of Lucy, the Unknown Man killed her in a fit of rage over what he saw as her uselessness. After Mayu had summoned Bando, who drove the Unknown Man away, Bando agreed to bury her corpse down by the beach respectfully. Since a battle between him and Lucy quickly followed this, the exact fate of her body is unknown.
At the end of Volume 1, an unnamed Diclonius is watched by Kurama and declared useless for their efforts to recapture Lucy. While it is possible that this was Nana, it also seems possible that this was #28.
Aside from Lucy, Number 28 appears to have been the oldest Diclonius present in the series. However, since she is a Silpelit, she must be much younger than she looks, making her tale that much more horrifying. Her physical age also casts doubt on the Silpelits numbering according to their order of birth, as her number is higher than the other known Silpelits, barring Mariko's number. If the Silpelits' placement occurred by order of birth, #7 (Nana) should be far older than #28, yet this does not appear to be the case. Given the potentially deadly nature of the experiments performed, it seems possible that Nana was not the Original # 7, but was given her room when she did not survive.
Number 28's life and fate somewhat resemble that of the X-Men's time-jumping member, Rachel Summers (Sometimes called Rachel Grey), known variously as Phoenix or Marvel Girl (the second X-character to bear these names, the first being her currently deceased alt-timeline mother, Jean Grey). Rachel escaped to the present-day from a future where mutants were being hunted to extinction by robotic Sentinels. A sadistic cyborg calling himself Ahab had Rachel, a telepath with the ability to sense other mutants, conditioned to be a 'Hound' and used to hunt other mutants down, her face bearing the marks of this brainwashing's branding. Luckier by far than 28, Rachel was rescued by her timeline's Kitty Pryde, who sent her back to the somewhat better present-day, where she has more or less remained since her introduction.
What is the cruelest act Humans committed against Diclonii?