Persona
Most, if not all of the Persona in Persona 3 are based on folklore and mythology. Mitsuru's two Persona are no exception. The rest of this section will explore the stories behind Penthesilea and Artemisia and how they relate to Mitsuru's character.
Penthesilea

In the Persona 3: Official Design Works book, the character designer states Penthesilea is indeed based on the Amazon Queen who battled and died at the hand of Achilles during the Trojan War. He comments that she is ferocious and elegantly beautiful. While Mitsuru's Penthesilea looks nothing like an Amazon, I think she certainly does retain elegance while clearly ready for battle.
I personally feel the major connection between Penthesilea and Mitsuru is the theme beautiful women can also be incredibly strong, too. Mitsuru doesn't necessarily look like someone who could walk into battle and be taken seriously with her thin and short stature, heels and manicured nails. Many do admire her for her beauty, but she is a force to be reckoned with both in and out of battle. Mitsuru is able to display leadership and fierce courage while fighting Shadows. Much like the Amazon Queen, however, she does temporarily lose her will to fight after her father is killed by Ikutsuki. She claims there is no longer meaning to her existence and doesn't see the point in continuing forward. Fortunately for Mitsuru, she is able to come to a resolution rather than seeking death and Penthesilea gives rise to Artemisia.
Artemisia

When I first read Artemisia was actually based on Artemis, I was at a loss for what possible connection the designers made to Mitsuru's character. After some thought and research, however, I am able to see some possible reasons why they may have chosen Artemis as a model. I feel that Artemis being known as an untamed spirit represents Mitsuru's character development after Penthesilea gives rise to Artemisia. Once she gains the resolution to continue fighting until the end, Mitsuru is no longer tied down by the past. It's almost as if a heavy weight is lifted from her shoulders and she is able to move about freely and independently. Artemis being the goddess who watches over children and childbirth is very representative of the Empress arcana itself as well. Being nurturing, compassionate and protecting are all motherly traits. Mitsuru may not always display it well, but I would certainly argue she is compassionate, caring and protective of those important to her. She also has strong leadership skills. Lastly, Mitsuru is very calm and collected, unlike Artemis' violent temperament. She does, however, have the capability to lash out "violently" if necessary and will not hesitate to "execute" others who have done wrong!
RESOURCES:
Artemis: Goddess of Light
Mortal Women of the Trojan War
Penthesilea @ Wikipedia
b a c k . c l e a r . f o r w a r d Resonance is © Samantha, however Akihiko, Mitsuru and Persona 3 are © Atlus and other rightful owners. Resonance is a part of AFTER-DEATH.ORG.