In the novel, Dracula had attacked her and forced her to drink his blood. This had connected her mind to Dracula's, allowing Abraham Van Helsing and the others to track his movements and follow him. In the end, Quincey Morris and Jonathan Harker kill Dracula, Mina subsequently regains her humanity, and later bears a son.
In Hellsing, the story references the original novel. Van Helsing defeats Dracula by punching a stake through his heart and successfully kills him, though later it is revealed that the Hellsing Organization took custody of his body, reviving the vampire as well as experimenting on him to make him the ultimate vampire. As such, Mina Harker returns to an apparently normal human after Alucard is killed, and dies of old age. However, it is revealed that the essence of Dracula remains within her corpse on a microscopic level, protecting it from some levels of decay as well as resisting even purification from holy water. Her corpse is exhumed by Millennium and experimented on by the Doctor, from which he manages to create pseudo-vampires that the Nazi organization uses. She first appears in Chapter 1 of "The Dawn" as a contorted figure wrapped in bandages and chained to a wall. She appears again in Chapter 2, in which The Doctor describes her as "perfect" and "horrible". He cannot believe that she exists, even after studying her. The Major refers to her as "our beginning and our end" and says that "once before, sanity and insanity fought over her," that "they trampled her underfoot," and that "she is just what is left over." It is assumed that "She" is the original vampire upon which all of Millennium's artificial vampires were based. In Hellsing, Chapter 93, "Sorcerian 2," the Doctor stands before a door marked "No. Anfang" (German for "beginning") and "She". It is implied that he is trying to release her, but doesn't know how to do so.
It is revealed in Chapter 94, "Oblivion", that because Dracula (later Alucard) did not die once he was defeated, the curse was still active within Mina Harker, which the Doctor exploited to create Millennium's vampires. However, since Mina hadn't absorbed anyone's blood and soul, she couldn't have been considered a true vampire. As such, the Doctor could not make vampires such as Alucard.
While "She" is considered the "corpse" of Mina Harker, the image of her mummified and bound in chains implies that at some point, she may have been alive while in captivity (perhaps in a similar fashion to Alucard's mummified state in the Hellsing manor). Despite that, her skeletal remains in "Sorcerian 2" suggests that she had been dead for quite some time.
- There is a metal seal in her skull written in the lower-right corner "SS Gestapo", Hitler's secret police service during World War II, implying the Gestapo was involved with Millennium for some time.
- According to Walter, Mina was the only vampire transformed by Alucard to drink Alucard's blood in return.
- During Alucard's flashback in OVA X, there is an image of Harker protecting Mina. While the picture isn't clear enough, the two of them resemble Seras and Pip.