Mukuro - Beyond the Darkness is the second Katekyo Hitman Reborn! Drama CD to be released. The story focuses on Mukuro Rokudo's inner thoughts towards all that happens to him before and after the Kokuyo Arc.
The story starts from Mukuro narrating his thoughts that he believes that there's no light in the world, as no matter where he looks from his previous lives, there would always be blood, violence, and darkness. From those experiences, he comes into conclusion that he knows that there's no light in the world and that he decided that he would color the entire world with darkness and strike against the world that created him.
The story skips to Kokuyo Land, Ken brings Mukuro to a theater, saying it's old but big and enough for them to live in. Mukuro comments that the place is perfect for a hideout and easy to set some traps, complimenting Ken as he looks around the room. Chikusa then interrupts them, asking Mukuro when they will make their next move. Mukuro explains that first, they need to identify who the tenth Vongola boss is, as they have very little information and only higher-ups of Vongola who knows the whereabouts of Vongola 10th. However, no matter how skillful, Mukuro is sure that a presence of mafia cannot be hidden, and there must be some followers of Vongola around. To make sure no one suspect of their actions, Mukuro ordered to relax for now and stabilize their status.
Afterward, Mukuro approaches Lancia, who immediately gives him a cold shoulder. Both of them starts to reminisce their past back when Lancia treated Mukuro like his little brother along with his Family. Lancia thinks that if he had known Mukuro's intention all along, he's sure that his Family would be alive by now. Mukuro, however, interjects, explaining that his intention from the very beginning was to control Lancia all along, angering Lancia. Mukuro then continues to say that he despises mafia, wishing to erase every single one of them from the world. Therefore, he reveals that their next opponent would be Vongola Famiglia, surprising Lancia. Mukuro tells Lancia to keep quiet for a while since they still have little information, but before Mukuro left, Lancia asked does his fixation towards mafia really true, since he has been possessed by him for long times, he could feel him at close range and realized that even though Mukuro says that he hates mafia, to him he looks so empty inside. This makes Lancia began to question what is Mukuro truly wants to destroy. Mukuro is amused by this and began to tell Lancia the 'darkness' within him and its distance. After he finishes, Mukuro asked Lancia is he afraid of him. Seeing that Lancia didn't reply, Mukuro orders him to fight and do as he commands as he leaves the room.
Meanwhile, Ken and Chikusa are trying Kokuyo Middle School uniform as they discussed their plans. During the discussion, Ken suddenly asks Chikusa why Mukuro saved them, both when they were children and when they escaped from the prison in Italy. Chikusa replies that he doesn't know, since it doesn't really matter to him as they will always follow Mukuro regardless of what they are to him, to which Ken agrees.
The story skips briefly to the battle at Kokuyo Land, showing Ken's battle with Yamamoto, Lancia's arrival, Mukuro reveals his true identity to Tsuna and the others, and lastly when Tsuna entered Hyper Dying Will Mode for the first time.
The story skips again to Tsuna working his homework at his room. Reborn notices that Tsuna stops writing and knocks him as he asked what was he thinking. Tsuna then asks what happened to Mukuro and his subordinates. Reborn reminds him not to worry about them, but Tsuna insists on knowing even though he couldn't forgive what they've done. However, Reborn ignores this and gives Tsuna more homework as he threatens to shoot him if he didn't do it, making Tsuna horrified and do as he says. Reborn discreetly thinks that Tsuna and Mukuro will meet again one day.
At Vindice prison, Mukuro, possessing Ken's body wakes up Chikusa and tells him surveillance cameras and guards are watching him, but with his abilities, he assures him that three of them could escape from the prison, but wait until he contacts him again and ready to go. Chikusa then states that somehow Mukuro is different from usual, which Mukuro admitted. He wonders himself is this also caused by the power of Vongola, and if it is, he wants it even more. Mukuro then asks Chikusa again will he come with him, and Chikusa answered he will and shortly the prison alarm rang along with running footsteps were heard.
The story ends with Mukuro thinks that he saw a glimpse of light when he battles Tsuna, wanting to make sure again with his own eyes that it wasn't an illusion, and he's sure that he will stand before Tsuna again one day, and until then he thinks it's not too bad to sleep within the darkness before awakened by the bright light.