Creating your own sexy anime girl is relatively simple because you do not need drawing skills to design your girl. Instead you need only a computer and an Internet connection to make a sexy anime girl using any anime girl creation website you prefer.
Write out your character's personality. Before you ever try making an anime character of your own, you need to give her personality. In anime, a character's personality will often carry over into the appearance of the character. For example, a character who is smart and bookish will usually wear glasses.
Open a web browser and select an online anime girl creation website or game. For example, go to Kongregate's Anime Character Maker or Anime Beach. (see References) The online anime creation games allow you to change the looks of the character to create your own anime girl character.
Change the character features and looks by clicking on the various options. For example, if you want your anime girl to have red hair, look under the area labelled "hair" and click on the red button. If you want green eyes, select the green colour under the area labelled "eyes." Change her look until she suits your preferences for a sexy anime girl character.
If you feel comfortable drawing up your own character, draw her personally. Start with the personality and design how you prefer her appearance.