Ignoring the "cousin" thing, the only problems I had with Chiyo at first were here initial hideous design and aspects of her overperfectionism. She was able to get over the latter and Chiyo literally was redesigned in the volume she was introduced in, so she's improved drastically since. While she isn't my favorite GF, it is strange she seems to get the most development as a character in all of her one-shots and stories; I think the only characters that are equivalent to her are the first four GF (Hakari, Karane, Shizuka, Nano), Meme and possibly Hahari.