Muraki's curse is a metaphor for AIDSHe gave the curse to Hisoka while abusing him, which, after years of illness, killed the young man. This implies Muraki is sick himself, and would explain why he's always trying to feed on the lifeforce of others, and is fascinated with immortality, yet isn't poetically associated with vampires. This has added weight, since the show is rife with gay overtones.
Chief Konoe was present for Tsuzuki's first descent into the insanity which lead to his suicide. He may have had a hand in it, which is why he's so tolerant and protective of Tsuzuki.
Hisoka is a girl.(I don't know if chapter 76 has been released or translated into English yet, so please excuse me if this has already been jossed/confirmed.) Ok, so we know that in Hisoka's family, the firstborn son has to take over as head. And it turns out that the current head, Nagare, had a daughter born first who was also named Hisoka. She was apparently killed as soon as she was born for being a girl, causing her mother to commit suicide and Nagare to take another wife who would give birth to the Hisoka we know. Tatsumi's original theory upon investigating the Kurosakis was that Hisoka was treated badly by Rui not only because of his powers, but also because he was the child of the first wife. So if we keep this idea in mind, the possibility that the girl Hisoka was kept alive and raised as a boy (a la Fruits Basket) seems much more likely. To back my theory up:
1. In the Hot Springs Episode, Hisoka refuses to join the other guys in the bath, not wanting them to see his body.
2. He's upset by the fact that, due to his death, his body won't develop any further physically.
3. Perhaps most damningly, Terazuma transforms whenever he touches a girl. In the tournament arc, he transforms upon touching Hisoka.
4. In a sidebar, when talking about the cast for the drama cd, the author mentions that she felt Hisoka should be played by a woman.
5. IIRC, the manga never shows Hisoka's bare chest.
Tsuzuki has angelic origin.
Alternatively, Tsuzuki is half kamiand the Count (or maybe even Enma himself) is his father. They do look rather similar from what we've seen so far. Being the son of a deity would explain his powers, such as the ability to control 12 of the most powerful Shikigami. The Count is also the Lord of the Castle of Candles; it should be easy for him to keep Tsuzuki's candle burning, thus effectively preventing him from dying while he was still mortal (until Enma interfered?). After the party in volume 9, the Count says that Tsuzuki's smile makes his life in the Castle easier (apparently he's imprisoned there - punishment?) and he asks the others to keep an eye on Tsuzuki for him. He even calls Tsuzuki "the only treasure he has left". Tsuzuki himself also says that "the aura of the Count felt somehow very familiar". As for the Count's behaviour towards Tsuzuki... maybe Enma wants to keep them apart, to eliminate any influence that might interfere with his grand schemes (whatever those may be) and this is the only 'inconspicuous' way he can be close to his son... yeah, it's a big stretch, I know.
Muraki killed Hisoka because he was hired by the Kurosaki family to break the family curse.Despite being a depraved murderer and rapist, Muraki appears to be a celebrated doctor in Japan with high-profile clientele. For centuries, the patriarch of the Kurosaki family has been cursed to be possessed by a vengeful god who rapes them on a daily basis. This was the fate that had awaited Hisoka had he not died. So it doesn’t seem so far-fetched to think that the Kurosaki’s may have hired Muraki to figure out a way to get out of their curse. After all, Muraki not only dabbled in dark magic but also genetic research and the supernatural in order to bring his brother Saki back to life. Not to mention being an actual doctor. If anyone could possibly figure out a way to break this horrific cycle, Muraki would’ve been the perfect candidate for the Kurosaki family to hire and figure out what to do. So Muraki accepted the job and researched how to possibly break the curse. Unfortunately, he realized it was either impossible or completely beyond his means to break the curse. After all, this was a literal god he was dealing with. Muraki has enough power to fight on equal ground with the Shinigami, but a god? Muraki would’ve realized that he didn’t have the power to take on Yatonokami directly without risking his own life. However, it’s also been shown in-series Muraki likes to see his projects all the way through to a very violent, bloody end and so he wouldn’t have simply given up and walked away from this assignment. So he came to the conclusion that the only way to break the Kurosaki curse would be the extinction of the family line. As Hisoka was the family heir and the next host, he would have to die so that there wouldn’t be another host for Yatonokami. It seemed too much of a coincidence that Hisoka was able to successfully sneak out the night he witnessed Muraki commit a murder. Perhaps that was due to Muraki’s intervention to lure Hisoka outside and kill him so nobody could save him? He probably also did not want to draw the attention of Yatonokami towards himself. Then who was the woman that Muraki killed? Muraki doesn’t kill without a reason. Maybe she was his assistant and he killed her so that nobody would find out about his plans? She might even have been just a stranger he found to kill to deliberately draw Hisoka’s attention towards him. Whatever the case, the fact that Hisoka was able to successfully sneak out and witness Muraki near the estate commit a murder seems too much like a coincidence. Muraki later claimed that he raped Hisoka and cursed him to die a slow, painful death over the course of three years because a “beautiful boy” like him deserved a special death. But maybe the method in which he killed Hisoka—raping him and subjecting him to slow, agonizing torture before eventually dying, was nothing more than a simulation of what the Kurosaki patriarch suffers daily from being possessed by Yatonokami? Despite erasing Hisoka’s memory of who cursed him to die, Muraki couldn’t just left the Kurosaki heir simply die and be spared the misery of being the plaything of a god. So this awful curse may have been nothing more than Muraki giving Hisoka a small taste of the nightmare that would’ve awaited him as an adult. To Muraki, this three-year long torture Hisoka suffered before he died was but a mercy compared to what his father constantly suffered. So while Muraki definitely crossed the Moral Event Horizon with his brutal murder of Hisoka, in his twisted mind he only saw it as a means to break the Kurosaki family curse. After all, with the family heir dead there would be no way for Yatonokami to be passed down to future generations and thus the Kurosaki family would no longer have to suffer under the possession of the god. As for what would happen if Yatonokami got loose without an heir to transfer to, well…Muraki probably knew of this possibility. But as he was only hired to break the curse, the risk of the god getting loose wouldn’t have mattered to him as it wasn’t his problem. So Muraki’s murder of Hisoka might have been a horrible case of “wrong place, wrong time”, or it may have been the conclusion Muraki came to that was the only way to end the Kurosaki family curse.