OOC: Explaining a plot
We thought it would be a good idea to explain the context of Muraki's recent log with Omi, especially given his murders already being a plot themselves. It may seem gratuitous on the surface, but we both have reasons for it as part of a larger thing between Muraki, Omi, and Aya.
Ever since their first conversation, Muraki has been fascinated with Aya because of his eyes -- canonically, violet eyes are extremely rare and he's obsessed with the one who has them, so it seems reasonable that he'd assume another person with the same color may be similar in some way. With no way to know how much power Aya has for him to add to his own and no real reason to pursue a lot of power, this has manifested as purely sexual interest and the desire to break him a little bit. He's stubborn enough that Muraki will get a lot of pleasure from both.
But Aya seems to have zero interest in or care for Muraki at all. This pushed Muraki to further measures.
Although he hadn't known what to do at first to force Aya to give him what he wanted, he learned quickly in an earlier log between the three -- Omi is close enough to him that they're moving in together and throughout their conversation, Aya did all he could to keep Muraki's attention away from Omi. On top of that, he called Muraki afterwards saying to leave him alone. Muraki's goal became clear because of all of that: use Omi to get to Aya.
So he waited until Omi closed Nectar alone, misjudged his skills in protecting himself, and still managed to get Omi to his apartment through use of his teleportation ability. Molesting Omi is both because Muraki sees sex and sexual violence as effective tools to use and because his plans include returning Omi visible unharmed, and with no memory of the event, but with the memories there in case he ever has a good reason to unseal them. This good reason will come after he's caught for his murders and feels like adding another person to the small pile of traumatized victims. It'll be just one more thing for him to be tried for, should Omi wish it.
As a result of proving that he could do any number of things to Omi if he wanted, Aya will give in to Muraki's demands and there will be one sex scene between them, leading to further resentment and more character development on both parts. It's also providing development for Omi, who'll have to deal with the aftermath of not remembering anything for a day and watching for changes in Aya later. The plot overall is to give all of them more things to do and more ways to develop in the face of unexpected experiences.