Nikk2009 said:

This is actually a great point. Why not just let the player make a Missionary from RT?

A Cleric from Macabeus Quintus or some similarly "hardcore" background should also fit the bill nicely.

The key here is the Ecclesiarchy can NOT have any males in official and standing martial roles. PERIOD! The Imperium is not a forgiving place, and given that most of the Imperium went to war over an Ecclesiarchy power-grab about 6 thousand years ago, directly leading to the formation of the Ordo Hereticus, the adamantine hull-plates of an Emperor class battleship will seem flexable and soft by comparison. Preachers? Sure. Missionaries? No problem. Deacons? Good. Warriors? HERESY!

The Frateris Militia is a very informal and temporary milita system, whereby the faithful are called to arms to defend the Church. Think of it like a bunch of farmers and mill workers rushing home to get their guns in times of crisis.

The Adepta Sororitas by contrast is quite formal (downright ritual!) and very much standing at perpetual readiness. They exist because of a legal technicality. The end of the Age of Apostasy was sealed with a formal treaty that FORBIDS the Ecclesiarchy from raising and maintaining "a standing force of MEN at arms." Therefore FEMALE warriors in service to the Church became legally acceptable, but MALE warriors in service to the Church are a crime and offence against the Holy Throne itself! Losing a civil war that was instigated by your own organization has consequences.... It is also interesting to note that many of the Adeptus Astartes chapters barely maintain a thin veneer of tolerance wrapped in scorn and disdain when it comes to interactions with the Sororitas. The Space Marines have LONG memories.

As already suggested before rather than thinking about "How can I fit a male Adepta Sororitas in the fluff?" turn the whole question around "What is the actual character idea and where can I fit it?". Assuming the original male character idea was based on Sisters of Battle, it would be something like:

- Religious fanatic

- Extensive combat-training

- Bolters, flamers, chainswords and meltas

- Organizational backing of Ecclesiarchy

Well, there is already a readymade package that includes all this. Its found in Inquisitors Handbook and called Black Priest of Maccabeus. If you don't want to use the cleric class, no worries, start with Guardsman and make him a "licenced-witch-hunter". A sort of ecclesiarchy witch-hunters who are organized to hunt down and burn witches on planet X. Yes, they are male. Yes, they have ecclesiarchy backing. No, they don't violate Decree Passive as they are a private organization (not funded by ecclesiarchy, but by "anonymous donators") and licenced by planetary governor.

Problem solved.

The Hobo Hunter said:

+1 Internet.

Also, there are no male variants of a true SoB.

The Imperium does not forgive those who want to be "different".