Kiriichimonji, like all other Shingu, was created four hundred years before the start of the series; the Emperor in charge of their creation had attempted to create weapons that would surpass the Teigu, but failed.
Kiriichimonji was kept hidden in the Empire's secret storage until It was given to Akame by Gozuki.
It has been stated that wounds inflicted using Kiriichimonji will never heal; otherwise, it has no other abilities.
Kiriichimonji's name can be interpreted as "cutting in a straight line".
↑ 1.01.1Akame ga Kill! Zeromanga; Chapter 3, page 11
↑ 2.02.12.2Akame ga Kill! Zeromanga; Chapter 4, page 22