(Advance notice: Alternate universe that takes place outside of Rebellion, where Nagisa actually survives. Given how little is known about wraiths and Madokami's new world, as well as Nagisa, I took some liberties for the sake of writing. Hopefully they're acceptable.)
Mitakihara City was generally quiet. Like most of human society, it wasn't without its troubles, yet there was always a benevolent guardian walking its streets. Mami Tomoe would spend each evening after her classes wandering around intersections, hospitals, bridges, anywhere where someone may try to hurt themselves or others.
She wasn't exactly what you would call a vigilante; her eyes were simply open to the world and the secrets behind human despair. She would hold her soul gem in her palm, and with a delicate step enter realms that were hidden to mortal eyes.
It was difficult to describe how magical girls like Mami fought the monsters known as wraiths. The demons were born of the hatred and woes of humans and would stalk them, invisible, until the person was driven to their death. They had a reality all of their own, shrouded in miasma, visible only to fighters such as Mami. Though they weren't typically very strong, they were many, and seeing a horde of their faceless figures could spark the beginnings of madness or terror in the weak or fragile-minded.
Mami was a veteran, however, and knew no more fear against the demons. She would raise her rifles against them without hesitation, determined to fight until her dying day, when the law of the cycle would come to claim her soul and ferry her to the beyond.
"I want to survive." Every battle, she reminded herself of her wish—or moreover her memories of it persisted in her mind. She was still alive and would continue fighting, no matter what, out of a sense of duty and justice. She had had acquaintances in the past, other magical girls whom she fought alongside, yet, without fail, each one insisted on going their own way, interested more in helping themselves than keeping company.
The one girl whom she had held closest to her heart eventually lost sight of their share sense of justice and nobility. Kyouko Sakura, the girl whom she had been prepared to call a sister, had even come forward to say she didn't really see them as friends, anymore. Her last attempt to reach out had resulted in Kyouko returning to her home town; she hadn't heard from her since.
That was about a year ago. Mami tried to hold memories of fonder times and mask her depression behind the facade of a normal, average school girl, yet deep down she understood that she was undeniably alone. No time for clubs or friends at school—not that she'd relate to her normal peers, anyway; no family to return home to: just herself and her apartment. The closest thing she had to a "friend" was the creature known as Kyubey, whom would often appear before hunting wraiths. His company wasn't unwelcome, yet his inability to comprehend human emotions sometimes unnerved Mami more than she needed.
On this particular night, she was tracing the signals of wraiths around a hospital. Kyubey had come with, walking by her feet. "The miasma seems to be coming from inside the building. The wraiths are probably inside. How do you plan to proceed?" the incubator asked.
"This might be a bit tricky," Mami confessed, brushing one of the twintails of her hair. "I may be able to enter through the visitor center, or slip in through one of the open windows." She scanned the side of the building. It was starting to get late, so most of the windows were closed. Temporarily dismissing that plan, she entered the lobby of the hospital.
Ghastly clouds of grief seemed to flood out of every corner, ignored and unseen by the nurses, doctors, and families in the waiting room. The demons were likely in the patients' rooms. Wraiths would feed off of depression and grief, amplifying the physical suffering a sick body might endure. Disgusting.
A nurse looked up from the desk, noticing Mami, "Good evening, are you here to see someone? Just a reminder visiting hours will be closing soon," she stated, almost robotically.
Mami absentmindedly nodded as Kyubey, unseen by normal humans, moved ahead, trying to find an area where the miasma was thick enough to enter so they might begin their work. "Yes, I'm here to visit," she quickly thought up a name to distract the nurse, "Ayako Mitsuya."
The nurse looked down, beginning to search the databases on her computer. "Mami, I've found a way in, come quickly," Kyubey called out telepathically. The nurse looked up, "I'm sorry, it doesn't appear that we have—" her voice trailed off as she noticed Mami was gone.
Fortunately there weren't many doctors around to see Mami slip by. She held her soul gem out in front of her, before a cloud of mist. He gem lit up as her magical girl garb materialized around her body, as around her reality began to slip away. By the time her feet touched the ground once more, she was in a pale, shadowy reflection of the hospital, with ghastly, disturbing moans echoing down its halls. Shadows of the humans in the real world still wandered through these halls, yet the wraiths were now physically manifested.
Which meant now they could be killed.
Kyubey jumped up onto Mami's shoulders as a rifle materialized in her hands. She began to step through the halls, listening intently, before taking a turn into a nearby room.
It was never a refreshing sight to see a wraith standing over the shadow of a human. Just barely visible in this alternate realm, a faint image of a person was still seen grieving, pained in their hospital bed, possibly sobbing. The wraith stood there, motionless until disturbed, ignoring Mami's presence, preoccupied with its "meal".
It finally turned its head, acknowledging Mami, who without hesitation raised her rifle and fired, piercing its head with a magical gunshot. The wraith vanished into dust, a few fragments of its curses falling to the ground, which Kyubey promptly swept up with his tail before returning to Mami.
The human's shadow appeared to stop writhing, beginning to rest easy. Mami smiled, satisfied, even if only temporarily—the gunshot alerted the rest of the wraiths in the area of her presence, and they were not prepared to go down without a fight.
The halls felt disproportionately large and open now, with demons coming out of all directions and rooms. Their sizes varied—many were larger than a human, a few even towered over Mami. A wraith's size depended upon how engorged they were with grief, violence, and despair. Regardless, this was child's play. Mami cast her arm aside, an onslaught of muskets spawning around her as they opened fire.
The first wave of the horde fell fast as more charge forward with eerie roars. Mami grabbed an spent rifle, turning it on its end to club the nearest horror before spawning a new weapon to blast the next in the face. She spun about, never missing a step or a shot, alternating between a strike and gunfire in a graceful ballet of death.
She wasn't afraid. Not anymore. A year or two ago she would have never thought to come to a hospital to face these odds, yet tonight she was in absolute control. Beast after beast dropped around her as she herself was unable to be scathed, until finally only one remained.
It was a large one, staring her down with its eyeless face, hesitating before striking. The wraith gave a growling moan, which Mami only returned with a small smile. She cast her arm up, a ribbon extending from it, as she whipped it forward. The ribbon coiled and let off a flash, transforming into a large cannon.
The hammer on the cannon came down, igniting the flint with a spark. "Tiro… finale!" she cried out, as it fired a generous blast straight through the wraith's core, banishing it in flames. The gun vanished after making its attack, as Mami relaxed her stance.
Kyubey immediately retrieved the curses that had been dropped, before Mami noticed something. "Why hasn't the miasma faded yet?" she asked as Kyubey returned to her shoulder once more.
"Perhaps you're not done. If a wraith is well distracted it may not have heeded your intrusion," Kyubey answered. "We can investigate further, or we can leave now—we have plenty of curses available for purification."
Of course Mami wasn't about to leave a demon unchecked. She stepped through the hall. It was a little unsettling to not know where one's enemy lay. Mami continued forward, listening intently. For the most part, the shadow world seemed quiet, muffled murmurs from the real world barely echoing to her ears. From what she could hear, none of it sounded distressed, at least to the point of being indicative of a wraith. Yet, before long she began to hear sobs.
She continued, following the whimpers. They were becoming more audible, beginning to couple with the groans of a wraith. Something didn't seem right, however; as she drew closer, the sobs became more and more clear.
She turned a corner before stopping at a door. The sounds were coming from inside. Slowly, she opened it. A wraith was standing over a figure as expected, yet surprisingly she could see another girl in the corner, cowering, staring at the wraith. She was fully visible, trapped in the miasma as well, wearing a brown hood and orange shawl, her hair pale white. The whimpers stopped as she went silent, looking at Mami, equally surprised to see another human.
The wraith, who had been ignoring the girl, turned from its feasting upon the human to look at Mami. Mami was still looking at the girl, too surprised to move. The wraith began to turn its form, moving to strike.
"W-watch out!" the girl squeaked. Mami snapped to her senses right at the wraith lunged. A small, double-barrel musket appeared in her hand as she blasted the wraith right in its face, inches before it reached her.
With that, the mist began to slowly recede. Reality flickered back about them, as Mami found herself in the hospital room of a very sick woman, a heart monitor letting off slow, weak beeps. The girl was still in the corner, not moved from before. Mami wasn't sure how to react, meeting her gaze, before deciding to dismiss her magical girl attire to return to her school uniform. As she expected, the girl likewise flickered in white light before her outfit faded away, leaving her in a simple pink dress.
"Ah, Nagisa Momoe," Kyubey broke the silence. "I did not expect you would still be here. Pardon us for intruding."
They stared at one another wordlessly, before being interrupted by a steady ring from the heart monitor. The woman's heart stopped, as the girl rushed to her side with panicked cries of "mama" between gasps and sudden, uncontrollable sobbing.
The doctors eventually came in and the woman was confirmed deceased. Nagisa was sitting in Mami's lap in one of the chairs of the room, using her shoulder to muffle her crying and dry her tears. Despite being a total stranger, Mami held her arms around the girl in an embrace, wanting nothing more than to alleviate her grief. One doctor, not recognizing Mami, turned to ask her for identification. "I'm Mami Momoe. I arrived a few minutes ago for my cousin, Nagisa Momoe," she lied, taking advantage of Kyubey's earlier identification, gently trying to comfort the crying girl in her arms by brushing her fingers through her hair. The doctor nodded, assuming the statement to be genuine based on Nagisa's reaction to Mami, and didn't bother the two of them further.
After a few hours, Mami was able to walk Nagisa out of the hospital. The crying had diminished to occasional sniffs and sobs, but Nagisa was able to explain as best she could:
Nagisa herself was born a sick child. Her health would dip in and out of stable as she was growing up, and as a result she was never able to sate her sweet tooth when young. To make matters worse, her mother had contracted a cancerous disease months back, and her health had been fluctuating just as much as Nagisa's. Yet, even in her lowest times, she only could lament the health of her daughter. Soon the disease had become so crippling that she had been confined to the hospital, her body taking a rapid decline. She stroked Nagisa's head, wishing that she could share some of Nagisa's favorite cheesecake one last time.
It was then when Kyubey appeared to Nagisa, and explained his offer. In her situation, there was no way she would refuse a wish. Her mother's words fresh in her mind, she wished to share such a desert. It was unknown if the contract was what restored Nagisa's health, or if it was simply the process of becoming a magical girl, but her mom awoke from resting to the pleasant surprise of cake which they cut into and were happy, despite the tears both of them were holding back.
After the meal, her mother insisted on resting, her energy having left her. Nagisa had noticed the aura of grief starting to overtake the hospital then, though before it shrouded her mother, Kyubey had asked her why she didn't wish to simply cure her mother.
The wraith that had been feasting on her mother's life was a byproduct of her grief and now-disappointed expectations. It was the first one Nagisa had faced, and she had been too afraid to act, convinced she had killed her own mother. If Mami hadn't arrived in time, she likely would have fallen to despair or been killed as soon as it had finished with her mother.
Mami had brought the girl to her apartment to give her something sweet to eat to hopefully alleviate some of her sadness. With a motherly sense of care, she also examined Nagisa's soul gem, using some of the surplus curses she had collected that night to purify the tears that earlier that day had begun to stain it black.
"Do you have any other family to stay with?" Mami asked tenderly, cautious about upsetting her further as Nagisa was helping herself to a slice of cake.
Nagisa paused her cake acquisition as she shook her head, crossing her feet on her pillow. "I don't have a dad… They wanted to put me in an orphanage." Her voice was starting to quaver slightly, as she felt a pit returning to her stomach. The cake sat untouched on her plate. "I'm scared…" Mami slid a little closer to her to offer her a hug. Nagisa nestled her head against Mami's chest, a few tears in her eyes as she whimpered, "I miss my mom…"
Mami cooed softly to her, stroking her head to try and pacify her. "I know you do…" The tears started to run down Nagisa's cheeks as she sniffed again. "I'm so sorry, Nagisa... I know what it's like..." Mami decided to chance an ask: "Would you like to stay with me, instead? At least for now."
Pausing briefly, Nagisa gave a wordless nod, nuzzling against Mami before hugging her tighter. Her voice was quiet and frail, "If it's okay..."
Mami gave a comforting smile. "I have a place for you to sleep, it's no trouble at all. Plus, we're both magical girls. It only makes sense that we would help each other, right?"
Nagisa gave a small nod, most of her sobbing finally quiet once more. She yawned, leaning on Mami's shoulder, her eyes fluttering. Though the day had been upsetting for her, she felt oddly safe with Mami, and was willing to let sleep overtake her.