A Girl with a Dream
Ayana Sakanagi is a young girl, being only 7 years old. As a child, she admired those who were in command and saw them as her leaders. She admired her teacher, who she would always try to emulate, and she admired anyone of a similar quality as well.
Ayana was interested in the social game Magical Girl Raising Project, and played it for a while, before its Mascot, Fav, had told her that she had been chosen to become a real-life Magical Girl. Accepting the role, Ayana became the Magical Girl known as Swim Swim.
On her first transformation, she was assigned to a mentor. This mentor was another Magical Girl, who dressed, behaved, and was named like a princess. Her mentor was a Magical Girl known as Ruler. During Ruler's first visit to Swim Swim, she had told her to obey every word that she says as if they are law. Swim Swim, respecting the position and power that Ruler had, kept those instructions to her heart.
The Elimination Game Begins
At some point, Fav announced that there were too many Magical Girls within N-City and that he's cutting the girls down to 8 using the Magical Candy system that he designed. While many of the girls were angered at this announcement, Swim Swim remained calm, as she believed following Ruler's orders would ensure their success.
Swim Swim and Team Ruler tried many things to achieve the highest candy amount, with Ruler being the most collector of candy in their team, and Swim Swim coming close to a second. Unfortunately, both the Peaky Angels as well as Tama were unable to collect many candies.
Luckily for Team Ruler, they weren't the lowest. It was, in fact, revealed at the end of the week that Nemurin had the lowest amount of magical candies, and was therefore eliminated from the group. That same night, Nemurin had transformed for the very last time and by chance, visited Swim Swim's dream. Within the dream, Swim Swim shared her ambition of becoming Ruler, as Ruler herself states that everyone must strive to become the leader. Nemurin encourages Swim Swim to fulfill her dreams, giving her the confidence she needs.
Unfortunately, Swim Swim's interpretation of becoming Ruler also meant that there could only be one leader, and if Ruler was the leader, there would be no way for Swim Swim to become like her, thus unable to fulfill Ruler's commands.
A few days later, it was discovered that eliminated Magical Girls will in fact die. This made many Magical Girls angry as Fav confirmed this fact and didn't deny it at all, continuing the competition. Afterwards, an update on the girl's Magical Phone allowed them to share candies with each other, whether they consented or not. With an ability to steal magical candies, Ruler devised a plan in order to secure their safety from eliminations.
Unknown to Ruler, Swim Swim herself had also created a plan. The heist involved stealing candy from the highest collector, Snow White. This supposedly would ensure their safety. Swim Swim, however, saw this as an opportunity to assassinate Ruler.
During the heist, as Swim Swim and Ruler ambushed Snow White in the tower where she normally met La Pucelle, Ruler had commanded Snow White not to move using her powers, and Swim Swim was assigned the task of stealing Snow White's candy.
Swim Swim stole a total of 25,000 candies from Snow White, who had a total of 50,000. After the theft, and with the arrival of La Pucelle, Swim Swim and Ruler had to retreat. During the retreat, the two were separated, with Ruler being with the Peaky Angels, and Swim Swim with Tama. Ruler, knowing that Swim Swim was safe, retreated to home base, with the hope that Swim Swim would also return back home.
Swim Swim, however, had deposited many of the magical candies to Tama, about 23,000, leaving only 2,000 candies in her possession. Swim Swim ordered Tama to ask Fav to divide the candies equally among the Magical Girls, save for Ruler, Snow White, and La Pucelle, knowing that this would place Ruler in the last place.
With her plan set, Swim Swim went back and gave Ruler her phone containing 2,000 candies. Ruler divided it unequally among the team, with Ruler getting the most candy. However, despite this, due to Swim Swim's plan, Ruler, in fact, had the least amount of magical candies in the end, resulting in her death.
Afterwards, Swim Swim buried Ruler's body, and the remaining members of the team unanimously agreed that Swim Swim would become the new leader of Team Ruler.
A Good Leader
After Swim Swim became the new leader, she set about leading based entirely on Ruler's words. She also made sure that her team was supported greatly, as Ruler has also said that good leaders should be respected. Because of the way she treats her team, individuals such as the Peaky Angels were more willing to follow her orders, as Swim Swim was seen as more benevolent than Ruler ever was.
However, another important rule that Swim Swim maintained was that strong opponents needed to be eliminated before they can become a threat. Swim Swim identified various individuals that matched this description. Most notably Weiss Winterprison and Calamity Mary.
At this time, Fav introduced several magical items that were on sale. These included a weapon, some medicine, as well as an invisibility cloak. All of these items cost lifespan, meaning each Magical Girl had to give up some amount of their possible years remaining in life. Swim Swim, believing that a leader must serve as a good example, purchased the most expensive ones, whilst her teammates only risked a small amount of years.
The weapon was given to Swim Swim, with the medicine given to the angels, and the cloak given to Tama. In honor of her mentor, Swim Swim named the weapon, a large single-bladed halberd, Ruler.
Eliminating the Competition
Following Ruler's words, Swim Swim planned out ways to take out the more powerful Magical Girls. Between Winterprison and Mary, the easier one to take out for her was Winterprison. She knew that Sister Nana had been sending out requests to meet other Magical Girls in an attempt to form an alliance. Swim Swim took advantage of these requests in order to lure Winterprison towards their base.
With Swim Swim confirming, the plan was set, and Nana and Winterprison arrived at the temple. Swim Swim had the Peaky Angels prepare themselves. Yunael disguised herself as Sister Nana, whilst Minael transformed into a knife at the ready. They waited and had hidden themselves in the invisibility cloak.
As Nana and Winterprison finally arrived, Swim Swim launched her trap, and the angels managed to mortally wound Winterprison and confuse her with their transformation. However, the angels reverted back, allowing Winterprison the chance to attack them. The ensuing battle killed Yunael, but as Winterprison attempted to finish off Minael, Swim Swim cut off Winterprison's hand with her recently acquired halberd. Both Swim Swim's team and Nana retreated from the scene, with Winterprison dying of blood loss.
Swim Swim blamed herself for not thinking of a perfect plan as Ruler should and losing Yunael in the process. The next target would have to be eliminated more cautiously. At this point, the only threat was Calamity Mary herself, and Swim Swim tried to figure out how to properly kill her, as she knew Mary is a dangerous opponent. Fortunately for her, Calamity Mary herself began an attack that would put her in the open.
The National Highway
It was here that Swim Swim and the other Magical Girls received a message on their Magical Phones about an attack on the National Highway. With almost all the Magical Girls gathering there for the possibility of collecting candies, Swim Swim decides that the chaos is the perfect time to eliminate one of them.
The team split up, with Swim Swim giving orders to kill anyone that shows a sign of weakness. Swim Swim saw Calamity Mary fighting with Ripple and Top Speed, and decided to wait out until their battle was over, and kill the survivor.
The fight ended with Ripple and Top Speed emerging victorious. As a result, Swim Swim, hiding this whole time, ambushed Top Speed and stabbed her in the back with her halberd. After a quick fight with Ripple, Swim Swim retreated to safety, and Top Speed died from her wounds.
At this point, they had supposedly reached the limit, however, Fav announced that due to the purchase of magical items, he will have to reduce the number of Magical Girls by 4, meaning Swim Swim's team had to figure out more Magical Girls to eliminate.
The Final Stretch
Minael launched a plot to kill the newest Magical Girl, Hardgore Alice, by sneaking in as her stuffed rabbit doll. Finding out where she lived and where she went to school, Minael and Swim Swim ambushed Alice in human form, ensuring that she can't transform into a Magical Girl in front of many people.
WIth Alice vulnerable, Swim Swim kills her with a stab from behind once more, using her halberd to do so, retreating as soon as the deed was done.
Afterwards, the next opponent that Swim Swim was after is Cranberry, the Forest Musician. Living in a secluded area in the forest, Swim Swim had very little to gauge with in terms of Cranberry's fighting potential. As a safety measure, they consumed the Healing Medicine they acquired beforehand.
Although they had planned to ambush Cranberry, the Forest Musician managed to outplay them thanks to her power to control sound. Here she also figured out that Swim Swim's powers, while valid on solid objects, can't work against sound-based attacks, and so Cranberry was actually able to hurt her.
In the ensuing fight, Cranberry managed to kill Minael and severely injure Swim Swim, to the point of the latter passing out and reverting back to human form. Upon seeing that Swim Swim is a 7-year old child, Cranberry froze for a split second, giving Tama enough time to scratch her and kill her.
Waking up, Swim Swim found herself safe with Tama. Tama had rescued Swim Swim, and in the process, had also seen her true form as a child. Knowing that one of Ruler's words is that a Magical Girl's identity should never be revealed, Swim Swim reluctantly killed Tama, decapitating her, despite regretting to do so.
The Last Ones Standing
With only 3 Magical Girls left, Fav attempted to make Swim Swim into his new partner, as Cranberry is now dead, and Fav wanted to continue what he did with the death games. Swim Swim declined, not understanding the purpose of Fav's proposition.
Angered, Fav engineered a meeting between Ripple and Swim Swim. Knowing that Ripple wanted revenge on Swim Swim. Ripple contacted Swim Swim, asking to meet in a duel. Swim Swim accepted, ready to duel with Ripple.
They met up in the dam, with Ripple wearing Top Speed's cloak. Swim Swim engaged Ripple by consuming Healing Medicine first, strengthening her body. The fight leaned towards Swim Swim's side, as Ripple had no way of physically hurting her, with Swim Swim managing to gouge Ripple's left eye.
Although Ripple couldn't manage to hurt Swim Swim due to her powers, Ripple had known her weakness from Fav, who saw Cranberry hurt her with sound. With this information, Ripple took a flashbang grenade, already enhanced by Calamity Mary, and used it to hurt Swim Swim enough to force her to transform into a human. The resulting blast also tore Ripple's left arm. With the last of her strength, Ripple tossed her katana towards Swim Swim's human form, impaling her in the chest and killing her in the process.
In the anime, Ripple was horrified upon learning that Swim Swim was just a child.
While the Magical Kingdom was able to pardon Ripple for killing Calamity Mary, they could not do so for killing Swim Swim, which was done for personal reasons. As a result, she would have issues getting into the Magical Kingdom.
Ripple was offered to have her left eye and restored using magic. However, she refused, leaving her handicapped.
Years later, when Ripple saw Pythie Frederica about to be killed by Rain Pow, she considered just letting her kill her and then get her through a surprise attack. However, she ultimately decided against it and saved Pythie because she didn't want to be like Swim Swim.