Sister Shannon Masters, a.k.a. Warrior Nun Areala, is a devout Catholic and an actual Catholic nun. She belongs to a centuries-old order of Warrior Nuns who serve the Vatican by defending the world against evil and supernatural threats.
Although Shannon Masters was born in the United States and her biological parents were Americans, she was raised in a Japanese family. The family was headed by an old Shinto priest (or Onmyoji) named Ota Yoma, who was essentially Shannon's adoptive father.
From: "Warrior Nun Areala" page on Wikipedia.org website (http://en.wikipedia.org/wiki/Warrior_Nun_Areala; viewed 30 May 2007):
Warrior Nun Areala collectively refers to a series of manga-style American comic books published by Antarctic Press. They were originally created by Ben Dunn in December 1994 (though the first appearence of their characters was in Ninja High School #38 1987) and and have endured on and off in various incarnations until the present day. The story revolves around Sister Shannon Masters of the Silver Cross, a fictional military order of Warrior Nuns and Magic Priests in service of the Catholic Church. The order was created in 1066 when a Valkyrie named Auria who renounced her pagan ways and turned to Jesus Christ for salvation; ever since then, Auria, now Areala, has chosen an avatar every generation to carry on the mission. In modern times, this has grown to a world spanning organization in the service of the Catholic Church with the current Areala, Sister Shannon Masters as the best and brightest. With her friends beside her, Sister Shannon has led the forces of good against those of evil, ever serving the Lord with faith and humility.
Ben Dunn, who attended a Catholic school, was inspired after reading a story about an order of New York City nuns who studied Judo and Taekwondo. He states that "Other superheroes, you never know what their faith is. Batman or Spider-Man or Superman, they do all these great things, but what do they believe in?"  In further explaining the concept, he added that "If Hell were an actual physical place with physical manifestations then they would be subject to some of the physical laws of nature would they not? Of course that would mean Heaven too would be physical place. While this may not be so in our world it certainly is so in WNA's world. Therefore, things would progress differently. To the Vatican in WNA's world 'thou shalt kick Satan's ass!'."  However, in creating the character, Dunn sought to distinguish Areala from scantily clad bad girl antiheroines with which she might be confused. However, he also stressed that "I made it a very strong point that she doesn't kill people, only demons," and that "She believes everybody -- no matter how bad they've been -- can be saved." 
Website Comicsutra states "That's what makes Warrior Nun Areala so special. At its core, it portrays people who have unshakable faith in God and their religion. .. Its affection for nuns is also evident - and sometimes returned. One real nun asked about Warrior Nun Areala noted that she and her colleagues give poor children college prep-level educations - that they are superheroes. Amen, sister." 
The story of the Warrior Nun Areala begins in 1066 with a Scandinavian girl named Auria who was born to a pagan father and a Christian mother. Impressed by her fighting prowess, Odin called her to serve as a Valkyrie; however, she was disillusioned when she saw that Odin would only accept warriors who had died in battle into Valhalla, even if they were wicked, and disregard good people who died peaceful deaths. In her own words, she would "not stay and serve a god of death! A god who would allow those with no honor to be his most prized warriors!" Due to this and to Loki's deceitful machinations, Auria then renounced her father's gods, dedicated herself to the God, the Holy Trinity, and waged a one-woman war against Asgard. At that, Yahweh, God Almighty--in her words "the only true God"--accepted her conversion and gave the former Valkyrie the Christian name Areala.
Though she was ultimately killed by Tyr, she was reunited with her mother and her father, who converted to Christianity shortly before his death, in Heaven. Now an angel of the Heavenly host, Areala was counseled by her mother to continue her work through others. That was she she saw a nun seeking to escape Viking raiders in Norway. On seeing this, she then felt no regrets at having left Valhalla and felt disgust at having been part of a pagan pantheon that would be, and was, destroyed regardless in Ragnarok. She gave the sister her name and power and, with the first Warrior Nun Areala thus empowered, the order of the Warrior Nuns was begun.
Sister Shannon Masters
Sister Shannon Masters, the Warrior Nun Areala, given the serial anature of her adventures has developed a wide circle of heroes around her making them into a family she otherwise would not have. That is seen in her foster sister joining the Warrior Nuns and her looking at her fellow Sisters as just that, sisters. Initially uncertain of herself she has developed as a charcter though she has never lost her idealism or her love of God and Jesus Christ. She has formed strong bonds of affection with her surrogate sisters, Sasuki, Mary, and Sarah; her surrogate son, Jason; her parent figures, Father Gomez and Mother Superion; and with them has fought a wide variety of foes such as Demon Foster, Julius Salvius, and Helga...
Notes and References
 "Super sister fights evil" USA Today May 5, 1997...
 Letter column Warrior Nun Areala: Rituals #4
 "Super sister fights evil" USA Today May 5, 1997
 "Cheap? Exploitive? Hypocritical? Nun of the Above." [link to: http://www.comicsutra.com/cs/stripped/strippedv1i30.htm]
From: David Wade, "Culture Watch: Holy Warrior Nuns, Batman! Comic books take on the world of faith and spirituality", published in Sojourner Magazine, July 2004 (http://www.sojo.net/index.cfm?action=magazine.article&issue=soj0407&article=040738; viewed 6 June 2006):
SOME OF THE most directly Christian characters in comics - and most interesting - are women. Catholic nuns have had numerous incarnations. A few years ago, Antarctic Press's Warrior Nun Areala drew much attention in the mainstream press. Employing the manga style of Japanese comics, Ben Dunn created a complete society within the Catholic Church of "magical priests" and "warrior nuns." They were equipped with traditional Christian as well as occult powers to fight the church's fight against evildoers throughout history, including an extended battle against Hitler during World War II. A darker manifestation of this idea is The Magdalena. Image Comics created a historical story that dated from the crucifixion when Mary Magdalene began a secret lineage of women warriors who fought against the enemies of the Lord while struggling with authorities within the church to control and manipulate members of their order...
None of these comics directly call their readers to repentance or make demands about church attendance. In fact, few of them have much good to say about established religion in general. What they add to the experience of their readers is the call to a life lived with at least one eye open to the possibility of an enchanted universe - a place where the spiritual world is alive, active, and intervening in the affairs of humanity. This intervention isn't in the form of brightly costumed messiah surrogates who can leap tall buildings in a single bound, but in the lives of fairly ordinary human beings, imperfect and often conflicted in their motivations, who are struggling to find meaning in their lives beyond the dulling drone of the culture's demands, the sudden storms of violence that threaten to overwhelm their worlds, and the limitations of life boxed in by not enough justice, not enough joy, and not enough hope. Out of this context, they become heroes. Just like you and me.
It's not just biff, bam, and pow anymore.
From: "Any Christian Superheroes?" thread began 22 April 2004 on rec.arts.comics.dc.universe newsgroup (http://groups.google.com/group/rec.arts.comics.dc.universe/browse_thread/thread/4e5839f075fecf76/8821b5db671e7ce1; viewed 20 June 2006):
From: Arnold Kim
Date: Thurs, Apr 22 2004 12:31 pm
re: "I can't think of any major superheroes that strongly believe in any real faith, and that surprises me. Certainly not in the DC Universe."
Nothing I can think of from DC or Marvel, and the only one that I can think of at all is Ben Dunn's Warrior Nun Areala (Antarctic Press).
Warrior Nun Areala - depends on the story arc, negative on the religion but positive on individual Christians, most usually.
From: "Gods and Champions" forum discussion, started 11 September 2004 on "HERO Games" website (http://www.herogames.com/forums/archive/index.php/t-21728.html; viewed 12 July 2007):
Sep 11th, '04, 04:46 AM
Doesn't it seem that religious based Superheroes get a sort of lopsided treatment? Characters like Thor, Hercules and others never seem to catch much flak for claiming to be pagan gods and such, but Christian based supers are either unheard of or portrayed as over zealous wack jobs. I'm not a particularly religious person so please don't take this a some sort of rant, just something I've noticed...
Sep 13th, '04, 12:28 PM
Warrior Nun Areala is fun in a quirky kind of way. The Catholic Church is still wealthy and powerful as ever because demons are known to walk the Earth and lead their minions such as the Demon Mafia. The Catholic Church has proven methods of fighting them. Their main soldiers are the warrior nuns and magic-priests. I didn't think it made fun of the Catholic Church in any way and the writer complied with a complaint from a real order of nuns that Areala's costume was too revealing.
Sep 13th, '04, 01:22 PM
[Posts picture of Warrior Nun Areala]
If this is the same "nun," about what issue # did they finally change her costume?
Sep 13th, '04, 02:17 PM
That's the one. I can't find any of the comics, but I've got a couple of trade paperbacks. I'll look in the #2 paperback: Rituals. In the plot, Areala nearly dies. While she's in coma, Mother Superior re-designs her outfit for more modesty. She explains that she never liked the old one due to its high '70s influence(Those mid-thigh slits up the sides:D). Understandable for a superhero comic book but inappropriate for a nun. BTW, her habit transformed into battle mode in a manner reminiscent of G-Force Transmute!) Anyway, an order of NY martial artist nuns complained and the writer got rid of the cleaveage and added leggings under the habit.
Sep 14th, '04, 09:08 AM
While I've never read the series, is this the "Warrior Nun" where she wears a habit that reveals cleavage and shows off pretty much all of her legs?
I've never quite understood the nun fetish thing, but I have to admit I liked Areala's costume.
Magdalena's too, actually. I guess it's the whole hood, cape, and skin thing they have going on.
Sep 14th, '04, 11:44 AM
To be honest, if I saw a woman dressed in Areala's old costume charging at me, I'd start looking for a weapon, not a motel phone number.
From: "Comics and Faith/Religion" forum discussion, started 12 August 2007 on Jinxworld website (http://www.606studios.com/bendisboard/showthread.php?t=122876; viewed 18 August 2007):
08-12-2007, 08:30 PM
I am looking for some new comics, or old ones I've missed, dealing with faith and religion. So far I have... I am looking more for mini-series. It need not be pro- or anti- religion, I am open to both. Suggestions?
08-12-2007, 09:29 PM
[Posts image: cover of Warrior Nun Areala: Portraits No. 1 (March 1998).]
08-12-2007, 11:06 PM
Well after numerous jokes it looks like the recommendations I'm considering are:
Man of the Atom