400 years ago, there was an Onna-bugeisha who lived her life as a retainer to a Lord. This Onna fell in love with a Miko that worked at a nearby shrine but the Onna kept her love secret, as the Miko was admired by many and it would damage her and her lord's reputation.
However, her Lord was allied with Oda and as a result, drew the wrath of Takeda. The Onna led her unit as best she could but the battle was lost. That's when she received the news that the temple had been raided.
The Onna abandoned her duty and fled the battle. As a result, the flank of the army collapsed and most of the surviving solders retreated to the castle. The Lord found out that she had fled and issued a kill on sight order.
The Onna made her way to the temple but her Miko was lying in a pool of blood. She dropped her weapon and held her. The Miko wearily opened her eyes and to her surprised saw the Onna crying.
The Onna confessed that she loved her and the Miko lifted a bloodied hand to the Onna's face.
"You should have told me sooner. I was waiting for you to tell me. And I'll continue to wait… in this life and the next…"
The Miko went limp. The Onna cried and hugged the body closer. The doors burst open and some of her fellow samurai recognized her. They charged at her. The Onna gently lay down the Miko, picked up her Naginata and charged into the fray.
2015, Sengoku Academy. A year two student is looking for a weapon to use in the upcoming Tournament. This Tournament is held every year and the winner gets to make a wish that the entire school has to follow.
For three years now, the queen of the school a girl with the surname Takeda, has wished for continued ruling of the school. She was to be graduating though but still she would fight to defend her title.
Others to challenge for the title included girls from such families as the Date, Shimazu, Hattori, Mori, Ueda and others.
The second year girl was a no-name girl from a no-name family. She fought last year and won against the Shimazu girl, gaining her respect and friendship but lost against Hattori.
The girl rummaged around the back of the gym storage room, which was filled with several broken and poor condition weapons. She managed to find an intact Naginata though. But it was in a glass case and it had a plaque that read:
"The weapon of a traitor."
The girl shrugged and opened the case. She touched the weapon and she paused. This weapon felt familiar. The rush of memories came back and she fainted.
She awoke soon after and looked around the room. She was here, a bit younger than before but touching her old weapon had awoken her old memories. She taught that she had to have been reincarnated. Given a second chance to save her Miko.
The new Onna picked up her old weapon and surveyed her surroundings. That's when she saw her. A second year student like her. She had noticed her in first year but she quickly faded from the Onna's attention. But now…
The girl looked just like her Miko.
It had to be her. This had to be fate the Onna thought.
The Onna resolved herself. She would win the tournament and finally ask the Miko girl out on a date.
The Shimazu girl notices the change in the Onna but doesn't make much of it. The Miko girl is also a friend of Shimazu, but she's the class rep, so she's indisposed often. The Miko gets introduced to the Onna and says she looks familiar but the Onna changes subject. They start to get along and the Onna has to distance herself from the Miko, who's increasingly showing affection to the Onna.
Sorry that it's a bit long, was on a roll here.