The Social Welfare Agency in Italy is not what it seems. Yes, it rescues young girls who have been brutalized, but it then brainwashes them and turns them into ruthless killers for an elite and secret counter-terrorism unit for the Italian government.

Enter a young girl named Henrietta. After witnessing the savage murder of her family and barely surviving, the Agency takes her in and repairs her injuries using the latest in cybernetic technology. All traces of Henrietta's past are wiped from her mind, as she becomes one of the Agency's most lethal assassins.

Gunslinger Girl had six volumes published in English by ADV Manga from December 29, 2003 to December 11, 2007, following several periods of hiatus. After the publisher went defunct, Seven Seas picked up the license, republishing the entire series with new translations and in an omnibus edition (with the exception of the last volume) from February 1, 2011 to July 2, 2013.