星の王女～宇宙意識に目覚めた義経～（Hoshi no Oujo ~Uchuu Ishiki ni Mezameta Yoshitsune~）

Her brother Shanaou was killed by a member of the Heike clan.
For vengeance and to restore the Minamoto clan, the protagonist Sakurako vows to destroy all the Heike.
Introducing herself as Shanaou in place of her late brother, along with her childhood friend Kisanta she goes off to Kurama Temple for training.

One day a merchant named Kichiji appeared in front of them. He had been told to come and pick them up by order of Fujiwara no Hidehara. In order to defeat the Heike, they couldn't afford to stay at this tranquil temple any longer... So Sakurako decided that they should go to Oushuu Hiraizumi where Fujiwara no Hidehara was waiting.

Hiraizumi where Hidehara ruled was a peaceful land that had no relation to war.
There the protagonist trained her sword arm in the dojo of the famed teacher Satou Tsugunobu.

However, Kichiji brought news that would smash that peace.
Sakurako's big brother Minamoto no Yoritomo, was raising an army to defeat the Heike.
She wanted to run to her brother's side immediately, but as she was now she was powerless.

Once again she went to the capital. To find a man whose name reached even Hiraizumi, the "Demon of Gojou", and become his retainer.

She advances deeply and quietly into an entangled destiny like many heroes before her.

[Translated from the official site]