May "Mayday" Parker is the first child of Peter and Mary Jane Parker in a future, alternate universe. Peter and Mary Jane were reunited with their baby daughter by Kaine, who found the child living with Alison Mongrain, the con-artist who had kidnapped the baby on instruction from the Green Goblin. After they were reunited, Peter lost a leg during a horrific battle with the Green Goblin. After the battle, Peter was offered a bionic replacement from Mr. Fantastic, and considering it a wake-up call, decided to retire and focus on being a husband and father. For years, they chose to keep their past from Mayday and hoped that she wouldn't develop powers of her own like her father.
Despite her parents' hopes, May began developing versions of her father's Spider-powers when she was fifteen. At the same time, Normie Osborn (the Green Goblin's grandson) set out to restore the family name (as he saw it). Mayday donned Ben Reilly's Spider-Man costume to stop him, but her worried parents burned the costume after May used it to keep her from taking on crime fighting.
Days later May was parting ways with her father from the police station when her spider-sense alerted her to a shady character who was stalking her father. She secretly nabbed the stalker, who was intending to kill her father, and beat him up in an alleyway with a trashcan without allowing him to see her identity. This threw the would-be-killer off of Peter's tail, and May got an addicting rush from saving someone's life.
Over dinner the same night, Peter told his family about the police case he was working on related to a string of murders in the fashion business. May used this info to investigate the fashion store her father was talking about, wondering if the villains behind the fashion murders were the same people trying to get at her dad. While investigating, May wore a makeshift costume from various pieces of black clothing she owned as well as the web-shooters she had saved from Ben Reilly's costume without her parents knowing. Upon arriving at the store she found a conversation happening between a mysterious villain named Nobody and his henchmen, one of which was the stalker hired to kill her father. While listening in, May was noticed by one of the henchmen, and a battle ensued in which she defeated the goons and Nobody (who used his powers to teleport away when the cops arrived). May rushed home to avoid being caught fighting crime by her parents. However, the escapade had inspired May to use her powers more, and over the next few days she secretly sewed herself a costume and christened herself "Spider-Girl". Eventually her parents accepted her crime fighting passion and began helping her.
May promised to give up costumed super heroics, dated Gene Thompson, and ran for student council president. When Mary Jane became aware that the Hobgoblin posed a threat to her daughter's teenage friends, she allowed Mayday to resume her activities as Spider-Girl (a situation they wanted to keep secret from Peter). After a battle with the Hobgoblin, May told her father the truth, and after a conversation with Mary Jane, they allowed May to resume her Spider-Girl identity.
After an attempt at helping the S.H.I.E.L.D. government agency, a case filled with a piece of the Carnage symbiote was released. It attached itself to May's friend Moose, who became the new Carnage. In exchange, Carnage would bond itself to Moose's terminally ill father, curing him in the process. Carnage caused a stir at May's school and kidnapped Peter and Baby Ben, forcing May to confront her friend. May tried to talk to Moose within the symbiote but failed, and it bonded with her brother Ben. Peter escaped as May battled the two symbiotes and gathered sonic gear that might have been able to defeat the symbiote. However it was May who used the weapons, thereby destroying the piece of the Carnage symbiote. Her success was not without a measure of collateral damage as well, however; not only was Moose furious at Spider-Girl for dooming his father, but the sonic weapon rendered Ben deaf, possibly permanently.
Ben's hearing was eventually restored thanks to the intervention of Normie Osborn. Normie later stumbled on one of Norman Osborn's former labs, and discovered a fluid tank containing what appeared to be a physical duplicate of Mayday Parker. Notes left behind by his grandfather indicated that this Mayday was the original he kidnapped years ago, hinting that the Mayday who had lived a full life was yet another clone.
Mayday continued to date Gene, but her jealousy over Gene's relationship with Simone enraged and confused her. She found some mild release from her problems due to her close friendship with Wes Westin, which in turn incensed Gene. During an encounter between the three in a bar, Gene almost knocked out Wes with a firm fist, but the punch was blocked by a concerned Mayday. Gene's punch being obstructed by Mayday humiliated him in front of his entire football team.
Mayday eventually started to feel the weight of her relationship, and chewed out Wes for intervening on her behalf. Wes, however, remained deeply concerned about Mayday and discovered a plot by Simone to blackmail Gene and discredit her in front of the entire high school. Meanwhile, Fury the Goblin Queen activated a signal that awakened the Mayday inhabiting the tank within Osborn's labs, and she escaped, confronting Mayday on the roof of her high school just as she was changing into Spider-Girl. The clone could mimic Mayday's clothing as well as her appearance.
Having been caught in the heart of an explosion that decimated New York City, a critically injured Mayday, her costume torn away by the impact, was rescued from the debris by Araña's forces. Araña, realizing that Mayday might not survive her ordeal, offered to merge with her, but she intervened in a vision quest that Mayday was undergoing, and by aiding her overcome a force she was meant to overcome alone. She obstructed Spider-Girl from uncovering whether or not she was the true Mayday. Araña successfully completed the merging and temporarily assumed control of Mayday's body, leaving Mayday and a third, blond woman who shared her name (possibly the spirit of Aunt May) trapped within her own subliminal consciousness before regaining control of her body.
Meanwhile, the clone assumed Mayday's life and picked up where she left off, however her presence deeply disturbed Benjy and a crestfallen Mayday also discovered that she had split up with Gene. Gene angrily retaliated when Mayday visited him, forcing her to take physical action and slam him through a table. She later received a call from Normie, telling her about the capture of Peter Parker, leading the clone into assuming the role of Spider-Girl.
The body-swapped Mayday in Araña tried to find Araña within her own body, who was using her body as a trap to defeat the Black Tarantula. However, the body-swapped May was found by the clone leading into a battle between the two of them, just as the body swapped Araña was lead into the lair of the Black Tarantula. The Black Tarantula was able to see through Araña's trick and nearly knocked her unconscious, just as May in Araña's body was knocked unconscious as well leading the two of them to recover their original bodies.
Meanwhile, Normie Osborn, along with Kaine, Phil Urich (in his Green Goblin Costume), Darkdevil, and Normie's wife Raptor, tried to rescue Peter Parker from Fury's hands, unaware of the the fact that Peter had absorbed the mind and memories of the original Norman Osborn. This led to a fight between the assembled heroes and Peter, now possessed by the Green Goblin. Mayday arrived just as Peter/Green Goblin reunited with the clone, who was revealed to have been genetically spliced with the DNA of the Venom symbiote, giving her the metamorphic powers displayed by Spidercide, but without the need for a host like normal symbiotes.
Bonding with his "daughter" (and, unintentionally, Spider-Girl), the possessed Peter declared himself as "The Goblin God" and began to go on a rampage, while Mayday found herself trapped within her father's mental psyche. With the aid of the spiritual avatar of her great-aunt May Parker, as well as flashbacks to the day she healed Normie Osborn's psychological scars, Mayday and Peter were able to overcome Norman in a psychic duel and convince the Brand New May that Mayday was a good person. Norman was seemingly defeated, but not before he denied Mayday the chance to discover whether or not she was the true daughter of Peter and Mary Jane, or the clone. Mary Jane was rescued from near-death by Benjy, who revealed he had developed organic webbing.
With the Brand New May uncertain of her place, Mayday proposed she become a member of the Parker family. Mary Jane agreed, though Peter distrusted her and objected to the idea. Mayday took a walk, reflecting on how her parents, baby brother, and potential new twin sister had overcome so much and truly become "An Amazing Spider-Man Family".
Her relationship with Wes, and the exposing of her face to the Black Tarantula, remained unresolved for a while. However, after her life is saved by April, she begins a relationship with Wes.
As part of the Great Hunt initiated by Morlun, his brother Daemos located May's family and Wes and immediately assaulted them, managing to badly wound May and damage Peter Parker's cybernetic leg. Peter, in an effort to save his daughter, collided with Daemos, knocking him clear. May managed to grab her brother, Benjy, and could only watch on in horror as her family members were cut down in front of her. Just then, two other Spider-Men opened a portal from another universe and beckoned May to join them. A tearful May then vowed vengeance on Daemos for the murder of her loved ones as she vanished.[8] She later accompanies Spider-UK, Spider-Ham, and Old Man Spider-Man to recruit the Peter Parker and other Spider Totems of Earth-616, revealing herself to him to convince him of the gravity of their situation.
Later, Benjy was revealed to be the Scion and was kidnapped by the Inheritors, 616 Peter promises May they'll get him back, but she angrily declares her father to be the true Spider-Man compared to the rest of them. When Uncle Ben tries to have a heart-to-heart with her, calling her out on the egotism of claiming her father is the only true Spider-Man and acting like she's the only one who lost loved ones, May attacks and berates him. Their fight is interrupted when a wall she cracked in a fit of rage crumbles and unleashes a horde of mutant spiders. The two set aside their disagreement and work together to contain the spiders, but May stubbornly refuses to let go of her desire for revenge against Daemos, stating that she hopes that somewhere an alternate version of herself exists who never had to suffer the loss of her loved ones. However, after witnessing the death of the Inheritors' Master Weaver, May realizes the cost of revenge and refuses to kill them, stating that she will seek justice rather than vengeance, with Spider-Ham commenting that, if her father was anything like him, he would be proud of his daughter. With the Inheritors defeated, May returned to her world with Uncle Ben, learning that her mother and Wes had survived the Inheritors' attack. As Ben chose to remain and be the grandfather he never had the chance to be, May decided to take on her father's costume and rename herself Spider-Woman.
However, it wasn't that easy: despite all of this, people still called her "Spider-Girl" and she hadn't gotten over her father's death, still wishing she had murdered Daemos when she had the chance. Using this against her, Enthralla and the Red Queen began ambushing other heroes with Enthralla hypnotizing them into thinking Mayday was an impostor who murdered Peter Parker and took his costume. Aided by her other hero friends and a late-to-the-party Ben, Mayday was able to stop the two villains, preventing a hypnotized Cassie Lang from killing her father and finally coming to grips with her own father's death in the process. She abandoned Peter's old costume and took up a brand new one, filled with renewed hope for the future.