It is the first year of the Genji era. A period of disorder that led to the downfall of the Edo shogunate.

The protagonist, born in the Aizu provincial family of samurai, lost her elder brother to war, and became orphaned at the age of sixteen.

Engulfed in sadness, she fell asleep one night whilst hugging the blade her brother disemboweled himself with.

Suddenly, a deity calling itself Byakko appeared in her dreams—

Byakko informed her that Aizu will eventually lose the war, and bestowed upon her a single mission:

"With this gun, please prevent the 'Tragedy of the Youth' from ever taking place.
If you are able to accomplish this, I shall grant any wish of yours on the following dawn."

When she awoke, her brother's blade had changed into a gun—

Three years later, the protagonist, who had become an expert in artillery, was led to meet with her comrades-in-arms, whom she will share her fate with.

Will the ending they reach be one of tragedy, glory, or perhaps...

—This is a story of the fight against a tragic history.