Black Butler Season 1/2 Explanation (Spoilers)

It's simple: when Ciel was between life and death, Sebastian had to retrieve his soul and the symbol of the pact was on his hand, but he no longer had it because it was cut off and someone else did it, that being Claude. Then Alois made a pact with Hannah stating that if Sebastian managed to kill Claude and retrieve Ciel's soul, then Ciel would be brought back to life, but he would be a devil like Sebastian. There you go :)

Spoiler alert

Hello, first of all, I wanted to answer the questions above here. Claude stole Ciel's soul when Sebastian tried to retrieve it. He failed because the pact marked on his hand was torn, so he was suspended. Also, you need to watch the whole season to understand instead of just stopping at a few episodes. Mrs. Red never came back to life. Ciel simply doesn't remember his aunt's death. That's why many had a funny look on their faces when he talked about it. Also, it should be noted that yes, he has no memory of what happened during the last 2 years in the anime. He remembers the dance with Lizzy simply because, just before becoming a demon, during the battle in the labyrinth, Ciel remembers everything. That's why Lizzy is happy to discover that Ciel has regained his memory. Now, do not rely on Netflix, as mentioned above, season 3 on Netflix is just OVA. That said, YES there is a season 3 called "Book of Circus" which completely follows the manga during their adventure at the circus.

In summary, Claude stole Ciel's soul, Sebastian brought it back to life but Ciel has forgotten everything from the first season. There is a fight between the 2 devils for Ciel's precious soul but Ciel ends up becoming a demon, due to a jealous kid of the importance that Ciel has in the eyes of the 2 demons, and orders Sebastian to serve him forever. The whole story surrounding the queen is just an invention for season 1 and season 2 is equally invented. The OVAs are out of context and there is indeed a real season 3 called "Book of Circus".