Hitomi is the name of a character from Masamune Shirow's manga Appleseed. She is a bioroid, or biological android. Essentially, this means that she is an artificial lifeform, created using genetically modified, cloned human DNA. In this manga, bioroids form the ruling class of the futuristic utopia known as Olympus. Hitomi works as an agent of this government, and at the start of the series, she was sent out into the wasteland outside of Olympus to recruit Deunan Knute and Briarios Hecatonchires, two mercenaries who were living in the post-war ruins, and who are the main characters of the manga.
Hitomi is an interesting character. At first glance, she seems somewhat of an airhead, the typical "dumb blonde" (although she has dark hair). However, she's presumably fairly intelligent (she is seen reading some fairly advanced-looking books, and apparently has some technical skills as well). Most likely, she is more like the typical naive robot characters seen everywhere in science fiction (at one point, she consults a sort of user's manual for instructions on how to behave in a social situation).
She's also rather cute, but also sexy as well. In fact, I've noticed that Hitomi's character design has changed significantly through the manga series, evolving along with Shirow's drawing style. In the first book, she looks quite young, perhaps no more than 13 or 14, with child-like features and a rather, um, undeveloped body. In the later books of the series, she is obviously considerably older than that, and no longer looks like a kid at all (particularly in a scene in book 3, which, depicts full frontal nudity). Even her outfits get more daring, and indeed she typically wears the most outrageous clothes of anyone in the series. This is probably the Shirow style that most people are familiar with--incredibly sexy women in very revealing clothes--and it's interesting to look back and realize that he wasn't always drawing in that style.
Indeed, Hitomi's very different from the "typical" Shirow woman. She's not a cop, she's not a badass (although she did take out a tank in the first book with just a single grenade) and she doesn't have a massive fetish for weapons and other gear. I'd have to say that, along with the cat-like bioroid Artemis Alpeia, Hitomi's probably my favorite character in that manga.