From left to right.
Luna is chaos. She does whatever she wants, completely impulsive, without thought of consequence. She is unchecked id.
Maple is very logical, and thoughtful. She is reasonable despite Luna's being unreasonable. However, the stupidity of the world which surrounds her tends to make her a bit of a malcontent.
Aria is a pollyanna. She is super optimistic in the bleakest of times, and always believes that Jesus will get her through anything.
Fannie has a deep anger at the world which unleashes itself in violent ways. So far, she's only appeared in one story, which is not yet uploaded.
September has not shown up yet, but she is a mysterious character who manipulates others for seemingly unknown reasons.