The story surrounds an aspiring singer, Shuichi Shindou, and his band, Bad Luck (formed with his best friend Hiroshi Nakano on guitar). Shuichi wants to become Japan's next big star, and follow in the footsteps of the famous idol Ryuichi Sakuma, lead singer of the now-disbanded legendary group Nittle Grasper. One evening, Shuuichi is looking over lyrics for a song he was writing when his paper is blown away by the wind and picked up by a tall, blonde stranger. The man dismisses Shuichi's hard work as garbage, which hurts Shuichi deeply. Despite his anger, he is intrigued by the stranger. This will be their first, but not last, encounter as Shuichi becomes fascinated by the stranger, who soon turns out to be the famous romance novelist, Eiri Yuki (real name: Uesugi). Both the manga and the anime follow this plot.
The manga is a quirky blend of over-the-top humor (Reiji's giant panda robot destroying parts of New York, Shuichi's explosive nosebleeds and ridiculous declarations of love, K's machine gun wake-up calls, Tohma's half-teasing come-ons, etc) and yaoi. The storyline is just serious enough to be compelling, but also contains elements of parody. The characters are often thrown into insane situations and in some scenes the art style is dramatically overdone for comedic effect, one of many of Murakami sensei's well know traits and characteristics in her manga styles.
The art style of the manga is notably different in volumes 1-5 than it is in volumes 6-12. The first half of the series has a more "old-fashioned" style that slowly changes and becomes noticeably different by volumes 6-7. The second half features cleaner lines, and more polished and stylish appearance. This also appears in the sequel, Gravitation EX, where each character's drawing style is drastically changed. For some, it's not very much except a little lolita-fication, but for others, you may have to see the name before you can recognize them. For example, Mika (Tohma's wife) was last seen in the early stages of pregnancy whereas now there is no visable evidence of such a state. There is also Shuichi's sister Maiko.