I've gotten into a habit of not naming characters; 10 of Diamonds is more of a title and indication of her relative power. I also call her Estoc after her weapon. Initial design inspiration came from Miki Sayaka and Kinomoto Sakura. The only rule to her functioning I've come up with is the idea of magical entities in her universe only being vulnerable to literally 'having their hearts pierced', hence the type of sword used. This isn't meant to have romantic connotations, rather blood is the source of one's power. As might then be expected, her outfit is mostly red, with some white and black. Under the diamond-studded part of her coat is actually a coat of plates worn to protect her own heart, and it's quite heavy even if it is supposed to materialise out of nowhere as these outfits do. So, what if she loses a limb and bleeds out? Well, that won't happen; she has control over the motion of her blood, and can even take the form of an entire pool of it to... well, drown her enemies, or something. Not a very pleasant power, I suppose, but the idea of a dark magical girl has its own appeal.
The skirts could have a better impression of size. I seem to have that problem with full-body drawings. Her outfit does in fact conscist on ten visible diamonds in this picture, if you'll excuse the design of the estoc's quillons: two on the hat ribbon; six on the coat; the cape clasp; and the shield itself. This wasn't intentional though; the coat is actually supposed to have ten down its front, but the other four are obscured by the cape and belt.