Kazuaki Mikado

About

He was the former fiance of Tsuyako, a college student, also being Hikaru's bigger brother (with different birth mother). His model character in "Tales of Genji" is Suzakuin. Although described as a gentle young man who would do no harm to anyone, he is feared by Tsuyako and Aoi.

Spoilers for volume 4

He is the one who actually inherent the "Spider Bloodstream" from the Udate family. He likes to dress in women's cloth and put on wigs to pretend to be a women with long black hair. Because of his feminize look, it's very hard to recognize him. He is responsible for kidnapping Aoi in volume 4 (with Tsuyako's unwillingly support), but Koremitsu managed to stop him at the last moment.
Spoilers for volume 6

In volume 6, he is shown as a member of the "Rose Clan" which rivals that of Asai and Fujino's "Fujihana Clan" in the Mikado family powerhouse struggle. He and Asai are both looking for the support from Gonomiya Orihime, who holds a large share of Mikado Corporation's stock. Both of them join a contest to write the best Japanese calligraphy to please Orihime, when Kazuaki is about to win, Koremitsu breaks in and wins the contest.
Spoilers for volume 9

He is the main "heroine" for volume 9 of the novel and also the mysterious black-haired woman on the cover of the same volume. He fund Yuu to go back to Japan to meet Koremitsu. At the same time, he also blackmailed Yuu by saying that she went back to Japan to sell drugs. It was later discovered by Honoka that the one who sells drug is actually Kazuaki himself dressed like Yuu. Kazuaki confessed that he did all these in reprisal of Koremitsu's previous deed, and of Hikaru not recognizing him because he is not a "woman." Koremitsu punished him but promised to be his friend in substitute of Hikaru. Kazuaki admit that he has feelings toward Koremitsu.

He feeds a chameleon named "San no Miya" (Based on Onna San no Miya in "Tale of Genji") and wants Koremitsu to marry to it at the end of volume 9.