There are several spoilers in this post, mostly in the synopsis section, but, even so, I don't reveal everything. Plus, there's some stuff you just have to see to get the full effect. The whole thing with what was done to Ciel's parents and the Queen will be sticking with me for a long time. Ick.
This show is set in Victorian England. Some time ago (months? years? I'm not sure), Ciel Phantomhive's parents were killed. Their bodies (body?) were burned up in a fire. Ciel was taken by a group of religious fanatics of some sort, but he managed to escape them by making a pact with a demon, who Ciel chose to call "Sebastian." Sebastian vows to protect Ciel, act as his perfect butler, and fulfill his wish to catch and kill his parents' murderer(s). In return, after Ciel's wish is fulfilled, Sebastian will be allowed to eat Ciel's soul.
Now that his father is dead, 12-year-old Ciel is the Earl of Phantomhive. He takes care of the family business (a toy factory) and serves as the Queen's dog, looking into and taking care of unusual problems for her. For instance, he investigates a town where people who don't obey the town rules turn up dead, supposedly mauled by some sort of spectral/demon dog. In another episode, he looks into the disappearances of young girls - and gets a lot of incentive to find the person responsible when his fiancee also goes missing. Well, I say that Ciel investigates things, but Sebastian does quite a bit as well. Whenever Ciel gets into trouble, he doesn't worry, because he knows that Sebastian will save him in order to protect what will one day belong to him.
Ciel's mansion has a strange cast of servants, nearly all of whom have a couple things in common - they're good in a fight and extremely loyal to Ciel and Sebastian. Aside from that, they suck as servants. Meirin, the maid, is extremely clumsy and can't seem to serve anything without tripping - her problem is probably her huge glasses, which she cherishes because Ciel gave them to her. In a fight, with her glasses off, Meirin is a lethal sniper whose only failing (if you want to call it that) is that she's too soft-hearted and couldn't kill a target who was playing with his young son. Bard, the cook who can't seem to make anything edible because he keeps trying to cook with dynamite, is an amazing soldier with a sixth sense that helps him survive dangerous situations, including one that could have been averted if his commanding officer had only listened to him. Finny, the sweet, bird-loving gardener, is so strong that he's more likely to accidentally rip a tree out of the ground than prune it. He used to be held captive by scientists who performed experiments on him that made him super strong. Tanaka is the only servant who knew Ciel before the events that took his parents' lives. Tanaka spends most of his time gently laughing to himself and drinking tea, but, when he pulls himself together, he's highly organized and knowledgeable.
Ciel's various investigations cause him to cross paths with shinigami (death gods), including a flamboyant red-haired one named Grell who would absolutely love to kiss Sebastian (with tongue) and maybe have his babies, never mind that they're both male. Sebastian is unamused, especially since Grell's adoration does not cause him to stop trying to shred Sebastian to bits with his chainsaw. Ciel also meets an angel who is obsessed with ridding the world of filth. He learns that this angel took his parents' bodies and sewed pieces of them together into one being, as a way of "purifying" them. What burned up in the fire was the abomination his parents had become.
Ciel now thinks he knows who Sebastian has to kill in order for his wish to be fulfilled, but there's more to it than Ciel realizes. It turns out that the Queen herself, as well as someone close to the Queen, is also responsible for his parents' deaths. Will Ciel be able to order Sebastian to kill the Queen, the one he has served so faithfully? As Ciel's determination wavers, so does Sebastian's desire to continue to serve as his butler. Eventually, Ciel finds himself alone, left to ponder how much he really wants revenge, how he wants to live his life, and what he really thinks is important. The answer he finally arrives at, as London is slowly engulfed in flames, causes Sebastian to return to his side. Sebastian fights the last being alive who is responsible for Ciel's parents' deaths and, by reverting to his true form (only shown in bits and pieces), is able to kill that being. His wish fulfilled, Ciel allows Sebastian to take his soul and his life (or so I assume, since the last episode ends while Sebastian is in the process of doing this), even though he knows that his death will probably upset his fiancee and his servants (if his servants are even still alive...).
There is also a one-episode OVA in which Ciel puts Sebastian in charge of making a charity play for children a success. The play is Hamlet, and Sebastian assigns the different parts to various characters from the show - Ciel, for instance, is Hamlet.
Much of the early humor in the show stems from Sebastian's over-the-top perfection. As long as Ciel orders him to do something, there is nothing he can't do, even if it seems physically impossible. He can save Ciel from murderous kidnappers in time (or, almost in time) to fix dinner, he can make award-winning curry (yes, there is a curry-making episode), and he can make a hell hound obey his commands. Ciel's servants' over-the-top mistakes are another source of humor, as are certain minor characters. My favorite minor character is probably Grell. Any episode with Grell in it was guaranteed to be one I would enjoy.
If you think the series sounds great and like something you'd enjoy, that's nice, but a word of warning first. This series has some shota aspects, although it never ventures into pornographic territory. Anything between Sebastian and Ciel is only implied - I'm pretty sure their relationship is only limited to master (Ciel) and deeply loyal servant (Sebastian). The thing is, Sebastian oozes constant sexiness, which means his conversations with Ciel have a tendency to feel intimate and often flirty. Plus, certain scenes are set up to make them look like something they're not. There's two main ones that come to mind. In one, Ciel is bent over with a flushed and pained expression. His shoulders are bare, which could mean that he's naked, or it could just mean that he has no shirt on. You might think, "oh my god, what's Sebastian doing to him?" - and then it's revealed that the scene is perfectly innocent and Sebastian is only dressing his master for their newest mission.
Episode 16 has another scene that is a bit off-putting. I have no problems with sexy shots of Sebastian, but sexy shots of Ciel are a bit...disturbing. In this episode, there's a scene right at the beginning where Ciel is taking a bath while discussing business with Sebastian. Eventually, he stands up, with the view from behind him making it clear that he's naked (no butt cheeks, but almost). As if that wasn't bad enough, then the view switches so that we're seeing Ciel's face...and the camera pans down his body a bit, fading into the next scene just before his genitals are shown (this may partly have been to show the seal on his side, but, if that's the case, it wouldn't have been necessary to pan down, a shot from the right distance away would've worked just as well).
In addition to those two scenes, there's plenty of instances of Sebastian practically fawning all over Ciel, fond looks (on Sebastian's part), face touching (again on Sebastian's part), etc. Ciel's, what, 12? If you don't mind that or can at least overlook it, then, by all means, watch this show if the rest of it sounds interesting to you.
Oh, that reminds me. Remember how I said that Sebastian oozes sexiness? Well, that results in actual sex in one instance - he seduces a nun at a cult and they have sex, although nothing much is shown, and it's more amusing than anything. That particular episode also hints at pedophilia on the part of the founder of the cult. Although I still have problems wrapping my brain around the idea that Sebastian can have sex (no matter how sexy he happens to be, I never expected anything to ever come of it), and the hints of pedophilia were disturbing, I had a happy moment during that episode when Grell got to cuddle up with Sebastian at the church. Sebastian didn't encourage him, but he didn't push him away, either. Oh, fangirl squeal.
In the earlier episodes of the show, Ciel seems very intelligent and almost adult in his maturity. He still has some vulnerabilities, but he covers them up as best he can and acts as much like a tiny, arrogant adult as possible. When Sebastian leaves him near the end of the series, however, he becomes pretty much useless. Even though he had shown, in earlier episodes, that he was capable of analyzing and handling murders and other crimes, without Sebastian he suddenly becomes too stupid to realize that, if he hands a guy a bag of money, the guy is going to try to rip him off. By that point of the series, I had come to sort of like Ciel (despite his annoying arrogance, his vulnerabilities and the revelations about his past made me feel sympathy for him), so I worried about how he would be able to manage on his own. I kept expecting Sebastian to show up and rescue him, and, at the same time, I kept wanting to yell at Ciel for not knowing how to handle anything on his own. I know, I know, with a servant like Sebastian, he would never have needed to learn how to take care of practical matters, but that didn't stop me from becoming annoyed with him.
Overall, I liked this show - but that doesn't mean I'd recommend it to lots of people, and that doesn't mean it'd come anywhere close to making it onto my personal "Top 10 Anime" list. Its various revelations were often bizarre, repulsive, and disturbing. However, thankfully, all that stuff came near the end of the series (or season, if what I heard about there being a second season in the works is true). By that time, I had come to like the characters, even if only on a superficial level, and I wanted to find out how things would turn out for everyone. I loved the humor, particularly when Sebastian and all of Ciel's other servants were together, or when Grell and Sebastian were together. Also, being very much an embarrassingly shallow fangirl, I liked Sebastian. I probably would've watched the series just for the whole "sexy demon butler" thing - all the rest was just icing on the cake.
The end of the show/season has a very "final" feel to it, so it's hard to imagine what a second season might look like, if there is, indeed, going to be one. If you find yourself wanting more after watching this season, however, there's also an OVA episode you might want to see. It has some of the weirdest stuff ever - a dog treat commercial featuring Pluto in human form, Hamlet done with just about all the non-villainous characters in the show (with Ranmao as seaweed), and a brief reimagining of the show set in the present day, at a sushi bar (Kuro-sushi). Bizarre.
Now for the watch-alike and read-alike suggestions. I had absolutely no problem coming up with things and probably could have listed more. The whole master-servant relationship thing is really popular in anime and manga.
Watch-alikes and Read-alikes:
- Loveless (anime TV series); Loveless (manga) by Yun Kouga - Twelve-year-old Ritsuka's life isn't very normal - his older brother died not too long ago, his mother is physically abusive, and a strange 19-year-old man named Soubi has shown up, claiming to have known his brother. Soubi says he is Ritsuka's Fighter, while Ritsuka is a Sacrifice. Ritsuka slowly comes to understand what this means, as he learns to battle other Fighter-Sacrifice pairs who may be able to lead him to knowledge about his brother's death. This is another show featuring a potentially inappropriate relationship between a man and a boy. Those who'd like something else with a master-servant relationship and a sexy male main character might want to try this.
- Emma (manga) by Kaoru Mori; Emma: A Victorian Romance (anime TV series), continues with Emma: A Victorian Romance Second Act (anime TV series) - The story is set in Victorian England. Emma is a maid and William is a member of the gentry. The two fall in love, but how can they have a future when their class differences keep pulling them apart? This series takes place in nearly the same time period as Black Butler and even includes some of the same locations, like the Crystal Palace. If Black Butler's setting interested you and you'd like something with a bit more historical accuracy and don't mind if it has an entirely different feel, you might want to try this.
- Hayate the Combat Butler (manga) by Kenjirou Hata; Hayate the Combat Butler (anime TV series); plus an OVA and another TV series - When Hayate's parents run up a huge debt, they decide to pay it off by selling him to the yakuza. Not particularly wanting to have his organs harvested for the black market, Hayate escapes and comes across a rich girl named Nagi. He decides to kidnap her for ransom money, but Nagi misunderstands him and thinks he has confessed his love to her. In the end, she finds out his situation, feels sorry for him, and pays off his parents' debt - however, Hayate must now be her butler for as long as it takes to repay the debt. Those who'd like something with butlers and humor might want to try this, particularly if you thought Black Butler was way too dark in tone.
- Godchild (manga) by Kaori Yuki - This series is set in 19th century England and stars Cain Hargreaves, the son of a wealthy count. After the untimely death of his father, Cain assumes the role of the head of the Hargreaves family, a noble family with a dark past. With the help of Riff, his faithful manservant, and Mary Weather, his beloved 10-year-old half sister, he investigates mysterious crimes. Those who'd like something similar to Black Butler in tone (the dark bits, not the humorous ones), with mysteries and a similar "icy young aristocrat, faithful servant" relationship, might want to try this.
- Blood+ (anime TV series) - Although most humans don't know it, humankind and Chiropterans, monsters that feed on the blood of the living, are at war. An organization known as the Red Shield tracks down Chiropterans and exterminates them. Saya believes she is an ordinary high school girl until she comes upon several Chiropterans at school one day and is encouraged to fight them by a mysterious man named Hagi (sometimes spelled Haji, which I prefer) who claims to be her Chevalier. Saya, who had had no memory of her life beyond the past year, begins to re-discover her past and her role in the fight against Chiropterans. Unfortunately, her formerly peaceful and idyllic family life is gradually destroyed beyond repair. Those who'd like another series with a master-servant relationship that has occasional romantic undertones might want to try this.
- Artemis Fowl (book) by Eoin Colfer - Artemis Fowl is a ruthless 12-year-old criminal mastermind. He decides to steal gold from the fairyfolk by kidnapping one of their own and holding her for ransom. What he didn't count on was that his kidnap victim, Captain Holly Short of the LEPrecon (Lower Elements Police Reconnaisance) unit, would be so much trouble. Those who'd like something else starring a smart, coldly intelligent child with an amazing bulter/bodyguard and emotional vulnerabilities where his parents are concerned might want to try this.
- Chrono Crusade (manga) by Daisuke Moriyama; Chrono Crusade (anime TV series) - Rosette is a nun who is part of a special demon extermination squad. As a child, she made a contract with the demon Chrono, allowing him to borrow her life energy in order to use his demon powers to their fullest extent. Together, Chrono and Rosette try to get Rosette's brother back from the demon Aion, an old friend and nemesis of Chrono's. If you like the "eventually fatal deal with a demon" aspect, you might want to try this. This series, like Black Butler, also features some humor and a historical time period (the 1920s).