Light Novel A girl (yaba) won't fit in a sheath (1) / Yu 龍威 Hero Library

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A 1 : 9 Male-to-Female Ratio in a Different World where the Values of Men and Women are Reversed? A Japanese fantasy where a young swordsman fights with young swordgirls! One day, Yuki Yu, born into a family of swordsmen, takes the life of his beloved girl for a certain reason. Although Yu must have killed himself as atonement, he wakes up in a strange forest. Wondering about it and wandering around in the forest, he meets a beautiful girl wearing a Japanese dress that is extremely sensational and cosplay. He thought that the girl who called herself "Kogitsune Maru" was an otaku who loved swords. Soon after that, he sees a strange monster, "Oni" and "Kogitsune Maru," who is able to defeat it, and he realizes that he has strayed into a different world. Listening to the story, it is said that human women are extinct in this world, and instead, a new breed born from swords, "Mitsuruhime-no-kami" is fighting with oni. Men who exist only about 10% of the population live under "Mitsuruhime-no-kami". Seeing girls who fight at the risk of their lives in a different world where the values of men and women are completely reversed, Yu proposes to fight himself too.