The Devil Six, Uninhibited is Chapter 107.5 of the Kuroshitsuji manga.
It is a special one-shot based on the results of the official Kuroshitsuji character popularity poll and dedicated to the "Devil Six" (Charles Grey, Vincent Phantomhive, Grell Sutcliff, Undertaker, Ciel Phantomhive, and Sebastian Michaelis), the rest of the top ten characters, as well as the characters whose rankings contain the number six.
Vincent thanks the readers and introduces the idea of a "Devil Six" story, saying that it involves a disaster.
Ciel, who is 2nd place in the popularity contest, receives an invitation from Viscount Druitt, who is 16th place, to attend his celebration banquet. Ciel does not want to go, but Sebastian, who is 1st place, says that Ciel should check out what "fun festivities" the viscount has in store and escort Elizabeth, who will be at the party too. Finnian, who is 10th place, and Snake, who is 7th place, are going to go as well. Baldroy and Mey-Rin, meanwhile, are too unpopular to be "shown in the panel."
Ciel, Sebastian, Finnian, and Snake attend the party together. Irene Diaz, a popular opera singer, is performing live. Lau is 9th place, Elizabeth is 8th, and her mother, Francis is 36th. They greet Ciel. Grey, who is 6th place, tugs on Ciel, telling him where the table for 6th place and up is and saying that they are waiting on him for the toast. They go over to the table, where Grell, who is 4th place, and Undertaker, who is 3rd place, are. Undertaker points out that Vincent, who is 5th place, is technically there too, though just as a portrait. Grell tells Sebastian to sit down at the table, but Sebastian refuses to because he is a butler and because he wants to be prepared in case of an emergency, implying that Undertaker is a threat.
Viscount Druitt steps out, and the Devil Six, except for Vincent, toast with him. The viscount then snaps his fingers, and a chandelier falls on the table. Sebastian saves Ciel, while the rest of them jump back. The viscount reveals that he has stolen Vincent's #5 rosette — basically, the higher leveled the rosette is, the more "powerful" it is. The rosettes can confer special powers to the owner that magnify their charm and abilities. The viscount wears on the rosette and transforms into a shōjo version of himself. Grey destroys an image of a younger Viscount Druitt in Weston College and tries to take the rosette for himself, but Elizabeth stops him. She and Finnian both want the rosette to grow stronger in order to protect Ciel. They and Grey chase after the rosette. While Grey and Elizabeth fight, Finnian wears on the rosette and becomes disproportionately muscular.
Snake wants the rosette to show Joker's 11th place rank and commands his snakes to take it. His snakes, however, bite him, in effect paralyzing him, and steal his #7 rosette, gaining the ability to speak. They want the rosettes from the higher-ups to grow hands and feet, and go after Finnian and Grey. Finnian is eager to fight them while Grey is terrified.
Grell attacks Sebastian, wanting Ciel's #2 rosette to transform into a "charming lady." They battle. The snakes end up stealing Ciel's #2 rosette. They combine and transform into a serpent, which begins heading down the street to wreak havoc. Grell talks about chopping it up, but Grey refuses to fight it. Ciel suggests that they all give their rosettes to Sebastian, to boost his power enough for him to fight the serpent. After the rosettes are attached to Sebastian's back, Sebastian fights the serpent and shoots a laser into its mouth, defeating it.
Then, Sebastian returns the #2 rosette to Ciel and reveals that he has already prepared dinner. Lau suddenly pops up, and Ciel asks him where he was the whole time. He lies that he was there with them, but Ciel does not believe him. Lau then calls Sebastian a hero. Sebastian denies that, saying that he is just one hell of a butler.
While the others enjoy dinner, Undertaker goes to Vincent's portrait and puts his #3 rosette on it, in a vain attempt to revive him.
Vincent, with the #3 rosette, tells the readers that love, though magnificent, can also give birth to a tragedy. He asks the readers to watch over his son's fate and removes the rosette.