Firstly, I will say that this is a well done drawing. The outfit is spot on when I compare it to an original picture of Len/Ren I have with me. The sky blue background helps accent and emphasis the white orbs that she seems to be playing with.
Your colour choice for Len/Ren is what I personally find makes this picture stand out. You've gone away from the traditional navy blue or pure black that Len/Ren is often seen in and opted for a more striking purple (Almost akin to Bougainvillea purple).
Her face is interesting in that it seems to hallmark this particular piece as your own, at the same time going against the traditional anime style faces. I particularly like how the face can be used for either a male or female character provided you know how to draw or position the eyebrows and eyelashes.
On the whole, nice work in the accenting and highlights of the character (Folds in the clothes, portrayal of movement), overall concept and the few personal touches to the piece.