The Butler, Vanished is Chapter 133 of the Kuroshitsuji manga.
Ciel, Tanaka, and some others try to get "Ciel" out of his bed as the twins' lessons are going to start soon. However, "Ciel" stays stubborn and declares that he will not study anymore. Ciel and Tanaka are at a loss with "Ciel"'s behavior, and upon hearing their son's tantrum, Vincent and Rachel arrive.
Ciel tells them what is going on, and Rachel says that he should go ahead to his lesson and that they would take care of everything. When everyone except Rachel and Vincent is gone, she tries to talk to "Ciel" but he interrupts her and yells that, no matter what, he will not go to his studies. Then, Vincent and Rachel nicely ask their son what his reasons for his decision are and tell him that they will not be angry with him.
After a while, "Ciel" mumbles an answer, and Rachel says that he should come out from under his blanket first before talking. He does so and cries while he entrusts his parents about Ciel's wish of wanting to open a toy shop in London instead of becoming a vicar in the nearby village. "Ciel" goes on how Ciel wants to leave him and how, because of that, he himself does not want to study anymore as he wants to be a toyseller alongside his brother instead of an earl. Baffled at "Ciel"'s outburst, Vincent and Rachel listen to his words.
Rachel embraces her son and tells him that she felt the same when she had to separate from her sister after marrying into the Phantomhive family. Then, she asks Vincent if she can borrow the blue Phantomhive ring from him. He gives it to her, and she hands it to "Ciel". Rachel says that this ring is very special and that only the Earl of Phantomhive may ever wear it and that only he can succeed his father. Vincent adds that neither "Ciel" nor Ciel will have it easy to become a toyseller—however, in the future, "Ciel" as the new Earl of Phantomhive may be able to support Ciel. Rachel agrees and says that, even if they are separated, they will be brothers forever. Hesitating, "Ciel" tells his parents that he has now understood that he has no choice.
The years pass, and on December 14, 1885, the twins wake up on their birthday and open the advent calendar for the day, taking out two rabbit fèves. Later, they head downstairs and marvel at the beautiful decoration and the numerous presents for them under the tree. They are congratulated by their parents and get the day off their studies.
After a while, Ciel and "Ciel" go to the kitchen to see what kind of cake the servants are preparing. However, they are sent out after Tanaka tells them that he will come to their room at six o'clock to help them change. Happily, they head back and fall asleep after playing. They wake up at six but nobody is coming to get them. Even after fifteen and forty-three minutes, Tanaka still has not arrived, making the twins worry.