Maki is a beauty, isn't she?
Maki isn't a character with as extensive a background as Kanna and Asuka, but I also like characters who are just there to have fun or help others develop. Maki is a perfect example of this, with a strong personality, a good sense of humor, and a slightly inexpressive nature.
She treats some customers with disgust, but is that how she feels, or does she just know that customer's nature and act accordingly?
Maki is the most experienced of the girls in the group when it comes to making a man feel comfortable, so she will add a lot to the coffee shop, and she feels comfortable around Haru mainly because she feels that they have extremely similar personalities.
Maki will be the most important character in teaching the other characters how to treat customers. Kanna and Shion are in good hands; Haru and Maki will teach them many things... while Asuka already knows exactly what to do.