Though it is a cool idea to work with established mythological characters, you also have to keep in mind that these characters are [LITERALLY] epic.

I like the use of a nickname for one of the characters with a particularly exotic name, it makes more sense with the modern setting, and makes the speech seem more casual. The way Echo speaks makes it seem more like she is talking to someone she does not know well, and yet from the dialog itself they know each other very well. Also, she is taking a very passive stance, and the pigtailed character with the pointy nose seems like a more dominant speaker, and yet Echo is rattling out a long piece of dialog without being interrupted as though she is also dominant in the conversation despite looking very shy and nervous. Though I have to say it does draw attention towards the character in the blue shirt since she is so balanced out and only says things that are short and interesting, and she has a lot of personality compared to the one in the turtleneck. (Poor Echo, though, she has the short end of the stick, and I love how you incorporated that so fluidly that at first I thought it wasn't in there.)

In terms of the actual art, it is expressive but the way the faces are drawn is very crowded looking. In a lot of parts people's mouths look like they are going to slide off the sides of their faces, and I am unsure as to why you chose to do that as it did seem intentional. You have a lot of great poses for hands but sometimes hands or parts of hands are the wrong size, such as the middle knuckles of the ring and pinky fingers in the closeup of the first hand are too long and that thumb is too short. In the next frame the girl with the blue top has hands that look like they would be bigger than her face. In the next frame the blond one suddenly has a very large hand, and the one in red would have an upcurved line leading from her hand to her thumb since it is stretching around something round. Things like that.

The blending of the shading is very pretty, but the shading is not always in the right places. In some places it looks like most of the light is coming from outside, and in others it looks like most is from above, and in others I can't even guess where the light is.

I have another comment which is more of an opinion than a critique, so I will put it in the comments. Enjoy critique week!