Isekai Samurai, Vol. 1 — Keigo Saito

As the final years of the Sengoku period dwindle away, Ginko, the strongest swordsman of the era, has yet to find a worthy opponent to slake her thirst for a fight to the death. Just when she's finally lost hope that anyone stronger than her exists, she gets transported to another world! And the first thing Ginko sees there is—a dragon?!