Personality and background
Shigure is laid-back and anything but solemn. He is a flirt, a tease, and often acts like a pervert. Akito once remarked, that, "I thought you'd sleep with any woman." He likes to tease Tohru about going on a date with her, and also says he likes high school girls. As a writer of both romance novels and academic books, Shigure loves to drive his editor, Mitchan, insane. His most famous and well-celebrated pen name is Kiritani Noa (western order, Noa Kiritani), which he usually uses for his romance novels, as 'Summer-Colored Sigh,' which he showed to Saki Hanajima, Arisa Uotani and Kyo Sohma. They give very different reactions, Hanajima asks if a sequel will be coming out, while Uotani says it is unacceptable to write that 'smut' and Kyo comments that it's sick. Tohru thinks it's amazing that she knows an author. Usually, he makes the editor suicidal by telling her that he didn't write anything yet, though he is finished already.
Shigure's best friends are Hatori Sohma and Ayame Sohma. This trio has been friends since their childhood. Together their nickname is the Mabudachi Trio. While Ayame and Shigure get along very well, it's less certain how Hatori, who is always exasperated with them, became their friend.
Occasionally, Shigure shows that he has another side to himself. He can be surprisingly mature, thoughtful, and gives rather sage and insightful advice to Tohru, Kyo, Yuki, and other characters, acting like an actual "adult". Only in the manga is it revealed that he is also quite cunning and somewhat dark-humoured. It could be said that in some ways Shigure is the one who is most affected by the curse, being in love with Akito and at the same time considered beneath her. It is also speculated and revealed in the manga that, although he does feel brotherly affection for her, Shigure is actually using Tohru Honda to break the Sohma curse. This is not true in the anime. Shigure is normally seen in a traditional kimono. Occasionally when he does business, he wears western style cothing (a suit). Naturally Shigure wears either a gray robe or a navy kimono. In the house, he normally walks around bare-footed while everyone else wears socks. He has his specific reasons for doing so, since it is his house.
Along with such behaviors, it is evident in both the anime and the manga (although much more noticeable in the manga) that Shigure is extremely manipulative, and would, in reality, use anyone and anything to reach his goal. He also is spiteful, having slept with Ren Sohma, Akito's mother, to get back at Akito after she slept with Kureno.
Shigure is in love with Akito Sohma in the manga. He has previously dated Mayuko Shiraki (Tohru, Yuki, Kyo, Uotani and Hanajima's classroom teacher), though nothing came of it and the relationship began probably because he pitied Mayuko's loneliness. He continues to antagonize her by appearing and interfering with her life with his machinations bringing her closer to Hatori Sohma, for whom she has strong feelings.
He is also noted for having a love affair with Ren Sohma, Akito Sohma's mother, on the basis that Akito had chosen Kureno Sohma over Shigure. Because of that incident, Shigure stated that he hated Kureno Sohma for having an affair with Akito. Akito, angry that he would have an affair with the person she hated most (her mother), kicked him out of the main house. In truth, it appears that Shigure actually loves Akito and has since they were both very young. His manipulations appear to be for the purpose of breaking the Jyūnishi curse, so that he can free Akito for himself; believing that the end of the curse will cause Akito to let go of the person her father wanted her to be and become her true self (just 'Akito', rather than 'God'). Shigure also states that he slept with Akito's mother, Ren, in part because she looked like what Akito could have been, if she had she been raised as a woman. In chapter 132, he confessed his feelings to Akito and kissed her.
In book 3, Shigure says he "had a dream about the one I love," referring to Akito
With Hatori and Ayame
The Three make up the Mabudachi trio, and was fond of getting into trouble along with Ayame. He and Ayame like to pretend to they're lovers, which freaks out Kyo Sohma to no end. He is described by Hatori "a jellyfish", and Hatori often seems exasperated with Shigure's antics. Sometimes, Hatori announces his displeasure with Shigure's manipulativeness, warning Shigure he will "one day push too hard."