Note:This is a review of the Funimation English dub version of this series.

Violence / Gore:
This anime focuses on a school where high school students are trained in weaponry. You'll constantly see people shooting/sword slashing at enemies, and even each other when someone gets angry (which happens pretty often). That said, this anime doesn't show a lot of actual bloodshed.
There is some brief comedy violence in this anime (i.e. girl kicks guy on head, he has a lump after).
The final episode of the series is the most violent. Blood splatters as characters are hurt, a spreading pool of blood is seen on the floor surrounding a body, and a girl is tortured Spoiler: by having a necklace forcibly shoved down her throat.
OVA note: In the special episode OVA, two bound women are shown hanging from a ceiling - they appear dead.

Nudity / Sexual Content:
In one episode, a group of girls wearing only their under garments flirt with their male teacher. Also, one girl technically lives with Kinji in his dorm (though she seems to have her own room).
Kinji goes into "hysteria mode" when he takes too much notice of the female form. I'm sure it's easy to imagine that Kinji is put into some pretty awkward situations to urge him into transforming.
Girls in their undergarments are shown many times. Female chests are often shoved into the main character's face. Lots of focus is put on female bodies.
Two girls are particularly sexual in their conversations. They both offer themselves to Kinji (very openly) multiple times. Some girls take their tops off in front of him or sit in his lap. One girl tricks Kinji into touching her breast.
Know that Kinji is not necessarily portrayed as perverse - he just keeps getting put into awkward situations.
OVA note: The OVA is a hot-spring episode that has a character standing nude - she is shown from the legs up (her rear is shown). Many girls in the hot spring are shown topless (the important parts of their chests are covered, but barely). Multiple conversations about breasts take place in this episode.

Potentially problematic theological themes:
One girl reads horoscopes. Some students have a "paranormal stealth ability" which leads to the use of supernatural powers.
A girl says she has a "devil side" ; a character is called a "demon."
In one episode, the sound of a human in pain is the catalyst that causes a monster to appear.
OVA note: The OVA focuses on a possibly haunted house and various paranormal instances take place.

Other potentially problematic themes:
Mild cursing (usually d*mn). Averages about 1 word per episode.


*Aria the Scarlet Ammo has an interesting storyline and memorable characters. While there is a lot of sexual content in this series, the two main characters seem to shy away from (or at least try to shy away from) sexual situations. Though Kinji changes demeanor when he goes into hysteria mode, he actually behaves like a gentleman rather than an out-of-control assassin.
This series is not a slapstick comedy, but does have some timely humor to balance the action. At only 12 episodes, Aria the Scarlet Ammo does end with a few plot points left opened for a future season/series.