The year is 2205. The "historical retrograde army(時間遡行軍)" has begun attacks on the past in their plot to change history. The government of Time(時の政府) recruits Saniwa(審神者), people who have the ability to animate legendary swords and travel into the past to defeat evil forces from their Honmaru(本丸/the core region of the castle, the place saniwa and touken-danshi live).

The sword spirits are called Touken-danshi(刀剣男士). They are like semi-gods and have the power to drive away and cleanse the impure sword spirits. Shino is one of Saniwa, and Suishinshi is one of Touken-danshi. 

On the day Shino becomes an official saniwa, she participates in the ritual to pick her first starter sword for her. But she found the lost sword on the floor and accidentally awakened Suishinshi Masahide, who is not supposed to be there or become anyone's starter sword...