The story follows six middle-aged men who have experienced success and failures in their lives. One day, they decide to become an idol group and overcome such barriers as their age and their physical condition.

Jing may appear to be a young boy, but his remarkable skills make him one of the most feared thieves on the planet. Along with his feathered partner Kir, Jing travels from town to town, stealing anything of value regardless of the amount of security. But when he's in a pinch, he has one more trick up his sleeve: Kir bonds with Jing's right arm to perform the effectively deadly "Kir Royale" attack. And because of all this, Jing is infamously known by many as the "King of Bandits."

Jiyu Nanohana is an ordinary schoolgirl until she runs across a scatterbrained 300 year old samurai who tells her that she is the reincarnation of Yagyu Jubei. With the help of the "Lovely Eyepatch" she transforms into the legendary swordsman whenever she needs to use his awesome fighting ability, which she needs to do quite often as a rival clan is dead set on conquering Yagyu to satisfy an old family grudge.

Misaki Takahashi is a regular high school student who is preparing for his university entrance exams. In order to reduce the stress of studying, or so he hopes, he accepts the help of his older brother's best friend, and famous author, Akihiko Usami. However, Masaki is about to find out that Usami's books are of a very naughty genre, and that there may be something naughty waking up inside Masaki as well. Junjou Romantica also follows the story of two other couples loosely connected to Masaki and Usami's "Romantica." Egoist shows the very passionate, but often complicated, relationship between university professor Hiroki Kamijou (whose life has reached an all time low) and paediatrician Nowaki Kusama, who falls for Hiroki at first sight and would do anything to make him happy. The third story, "Terrorist," shows just how obsessive love can become when rich eighteen-year-old Shinobu Takatsuki finally discovers something that he cannot have so easily—the literature professor You Miyagi. There is passion abound as these three couples try to achieve their goals in life while also falling into temptation and anguish with their partners.