Black Butler loves doing this with Ciel and Sebastian in the official art... and everywhere else.
Sebastian: I will follow you wherever you go, until the very end. Even If I were to be shattered in pieces, I would never leave your side. I would follow you to the depths of hell.
Sebastian's default habit of carrying Ciel bridal style, especially in the manga, and how he constantly rescues Ciel.
Let's not forget the (in)famous corset scene from chapter 8/episode 4...where it looked like Sebastian was having sex with a naked sweat covered Ciel from behind, complete with a blushing Ciel gasping out he "can't take anymore" and Sebastian telling Ciel to "bear with it." Of course, they're referring to Sebastian helping Ciel put on a corset.
Which was to enable Ciel to crossdress as a girl (wearing a frilly dress and sporting longer hair) so he could attend Aleister's party where he shared a dance with Sebastian who was wearing gentlemen's evening wear... Later on, Sebastian saves Ciel from being auctioned off by Aleister, even carrying him bridal style while he's wearing that frilly dress.
And then there's this, even though it seemed like there were other things to hide behind in that room... or they could have just ran out of the room, even.
Don't forget thesepages from Chapter 34 of the manga (it's vomit).
Is it bizarre to think so of the scene in Chapter 41 where Ciel straddles Sebastian's supposedly dead body, buries his face in Sebastian's throat and insists his butler was never to leave his side?
If anything, the entire purpose of Nina Hopkin's appearance in chapter 37 was to provide us with some comic relief, fanservice, shotacon, lolicon (meaning some Les Yay between her and Mey-Rin which includes kissing her and openly groping her breasts and thighs with some heavy breathing sound effects and hearts), and even more Ho Yay between Sebastian and Ciel (e.g. here, even though he could have just done this from the beginning...).
The beginning of episode 6 of season 2 has Sebastian appearing to be about to kiss Ciel (either before taking his soul or as a means of doing so), and he acts most possessive of Ciel (or Ciel's soul) declaring to Claude that "Young Master is mine." or "He is my young master." He also tells Claude that the fact that someone other than himself touched Ciel disgusts him as well as saying "The young master belongs to me."
Blatant even in the first opening theme of the anime, "Monochrome Kiss," which for some reason is a love song with some pretty provocative lyrics which are basically about someone falling in love with their saviour ("after I'd melted you tenderly saved me") and looking for some sign of affection from them even if it's hopeless ("netherless I search for a single form of love"). With our main duo Ciel and Sebastian as the focus of/only characters in the music video...It's actually kind of awkward to watch if you know what they're saying.
Not to mention that there's a rumour Sid wrote the song especially for the series.
In one instance, when Maylene thought that Sebastian was the one Ciel liked the most, she got noticeably jealous and coined Ciel as a possible "love rival".
Sebastian fighting over Ciel with Claude, which leads to both Alois and Grell implying that he's in love with Ciel. Sebastian doesn't deny it, and, in fact, agrees while fighting Claude in episode... 10? That he's not fighting for Ciel's soul...
In chapter 61 Sebastian goes berserk and attacks Undertaker when he threatens Ciel and Ciel and Sebastian have a moment where they reach for each other's hands but Undertaker attacks Sebastian before they can touch.
Chapter 62. Just ... Chapter 62. It contains a flashback about Sebastian's first day of serving Ciel, including giving him a bath for the first time - and getting quite touchy-feely with him. Just seefor yourself. Also, there's Ciel's Caught the Heart on His Sleeve moment with Sebastian in the same chapter.
Chapter 63: Sebastian doing the Hands On Approach when showing Ciel the proper way to shoot a gun. Also, his kissing Ciel's hand and both of them holding hands.
Chapter 64 gets its fair share, too. About half of the panels show Sebastian and Ciel having some kind of physical contact and in some, they hold onto each other very firmly. Sebastian's protective gestures seem almost tender, with one panel in which his fingers are entangled in Ciel's hair ... Oh, and there is another lovely shot of Ciel straddling Sebastian when he looks unconscious calling his name and looking overall concerned... until Sebastian says he's too loud and he's fine.
That scene in the anime where Sebastian saves Ciel from a statue thrown supposedly by Finny and cradles him in his arms holding him close almost looking like he's about to kiss him but fireworks (?) interrupt their moment.
Not to mention that the entirety of the above episode consisted of Ciel obsessing over finding out who Sebastian cared about the most (via magic camera). The episode concludes with the suggestion that Ciel cares most about Sebastian, much to Mei-Rin's displeasure.
In chapter 65 at one point, Sebastian again does the Bridal Carry to Ciel when saving him. Sebastian saves Ciel from the freezing water and gives him his coat to wear, trying to make sure he doesn't sleep or else he'll freeze. Also, Ciel says that he wants Sebastian to rest when they get back to the mansion, complimenting him and telling him that he did well. And in the last page Ciel and Sebastian look each other in the eyes.
Sebastian dances with Ciel in the anime in one scene.
Not to mention the fact that Sebastian reminds Ciel several times that he belongs to him. Physically.
At the end of the first anime when Sebastian leans into Ciel to devour his soul it looks as though soul-devouring requires some mouth action, but the scene just fades before he gets too close.
A bit of a meta example, but Ciel's English voice actress Brina Palencia believes that Ciel and Sebastian were in romantic love in addition to the master/servant relationship between them.
Don't forget Lau and Ciel. Madame Red even accuses Lau of trying to hit on her precious nephew way back in episode two of the anime and chapter six of the manga. Lau's answer leaves her less than reassured of his intentions.
And episode 6 has Ciel telling Lau that he has the option of returning to his own country. Lau shrugs off Ciel's statement and says "I still haven't run out of interest in this country." He then gets close to Ciel to whisper in his ear "Nor in you, Earl."
He also seems to enjoy carrying and teasing him.
And he also seems to be hitting on Ciel in some scenes.
In chapter 39, Ciel hosts a party with a lot of rich and powerful people present. One guest is a writer named Arthur Conan Doyle. Lau is also present at the party and when Ciel makes his presence known to his guests Arthur is shown to be shocked that a child is the Earl. Lau answers with "Yep, that tiny little child is Earl Phantomhive. Isn't he so cute?" And later, while the rest of the guests mingle and drink wine, Arthur goes and sits by himself, feeling left out. Sebastian comes up to him and offers him a drink. When Arthur looks up to thank him for the drink he is left speechless, blushes, and thinks "Wow....What beauty and ambiance he has. He could appear in a book by Oscar Wilde". And as Sebastian walks off, Arthur sees sparkles appear around him and stares after him in shock while blushing and thinking "I see, when you become top class, your servants are also top class..."
The following chapter (chapter 40) has Ciel being suspected of murder so everyone insists him and Arthur share the same bed that night. As an added bonus they're also handcuffed to each other, Arthur pats Ciel's head when he's feeling lonely, and worriedly watches a sleeping Ciel for a bit before falling asleep himself.
Also, take note of how Ciel is surprisingly nice to Arthur and smiles at him very often during chapter 39- considering this is Ciel and how he usually is with people, is really saying something. And at one point, Ciel and Sebastian are conversing in French and Arthur overhears them and laughs at one of Sebastian's quips, and when Ciel notices this, in response to Arthur's embarrassment he smirks and presses a finger to his lips- his expression seriously made him look like he was hitting on Arthur.
In episode 1 of season 2 when Alois sees Ciel he reacts with great excitement and says "Finally I have you, Ciel!"
In the 5th episode of season 2, Alois cross-dresses and flirts with Ciel via holding his hand, caressing his face, putting his hands behind his head, licking his ear, and outright telling Ciel that he "wants" him.
He also tells Ciel that if he's in pain he'll lick him to heal him up.
In the 6th episode of season 2, Alois intentionally provokes Ciel by dancing with his fiance Elizabeth and at the end of the episode they lock gazes with Ciel declaring "I will definitely kill you!" and Alois declaring "I will definitely make you mine!"
Episode 7, season 2: Alois straddling Ciel and getting close to his face.
As seen in the above picture, there's plenty of Ho Yay regarding these two in official art and of course fanart.
Alois's final wish results in Ciel's immortality. Aww!
Episode 6: Claude reminisces the last time he touched Ciel and remarks "The feel of him. One rarely encounters something so fine."
In episode 10, Claude is basically orgasming over Ciel, even going as far as to kiss his foot, while Sebastian is watching outside of the mansion with a some-what jealous face.
Before season 2 had even started, they gave us a lot of hints/fanservice in the scans (e.g. here).
In episode 1 of season 2, Alois begs Claude not to leave him alone, and Claude holds Alois's face in his hands and declares he'll never leave him alone.
In episode 8 of season 2, towards the end Alois tells Claude "I have only you. There's only you left in my world!" He then tearfully hugs Claude's leg and says "Don't ever leave my side! You are...you yourself are...My Highness!" It almost sounded like he was giving Claude a love confession. Claude tenderly holds Alois's face in his hands and leans in so close their lips are almost touching right before killing him.
In episode 11 of season 2, Alois tells Claude "Claude, you ensnared my heart in a spider web, my eternal Highness. I wanted your love".
And in episode 12 of season 2, Claude actually acknowledges Alois's wishes and it's hinted he will live on in love in the afterlife with him, Luca, and Hannah.
Claude/Alois is pretty much confirmed as of episode 12.
In the Spider's Intentions OVA Alois doesn't want Claude to ever leave his side.
As of his Character Development Alois appears to be Yandere for Claude and seems to actively do things to piss off Claude and get his attention.
Claude's catchphrase can even be interpreted roughly as "I want nothing but to deeply desire my master."
In a scene from episode 6 Claude gets really close to Alois's face and tells him "I want nothing but to devour you in one hell of a bite" or "I intend to make one hell of a feast out of you."
Soma and Agni count too. Their relationship really does come across as a Bodyguard Crush sometimes.
It's especially prominent whenever Agni starts crying about Soma, usually Tears of Blood.
Though this troper can't find the exact seiyuu event, there's a radio drama type thing with Sebastian conducting butler auditions — total crack setup, of course. Agni's audition ends with he and Soma going into a very John/Marcia name-calling exchange. "Soma-sama!" "Agni!" "Soma-sama!" "Agni!"
The lyrics to Agni and Soma's character song duet, Futari no Harmony, sound like a love song.
Ciel/Soma, Soma really wants to be his "best friend" and nursed him after his asthmatic attack. He also tends to carry and touch Ciel a lot.
In volume seven Soma is said to have stayed up all night nursing a bed-ridden Ciel.
In chapter 66 Soma is shown to get really worried when he thinks Ciel is having another asthma attack.
Soma also worried about Ciel to the point of crying in season two when he thought he had amnesia and always acts excited whenever he sees him.
There's also Sebastian/Agni too, especially when Sebastian seems rather happy about Agni calling him his "friend", since no one's ever called him that before.
In episode 6 in response to hearing Sebastian play beautiful sounds with some water glasses, Agni's response is to cry tears of joy, says Sebastian has an "immaculate soul", and then comments "How fabulous! You are a truly fabulous man, Sebastian!"
In the anime, Pluto (Pleute? Puru?) also gets a little bit of this with Sebastian, but that probably doesn't count since he's a dog. Who sometimes turns into a very fit, naked man, still with the mind of a dog.
Then there's Baron Kelvin's obsession with Ciel which may also count as No Yay, depending on how you look at it, considering the fact that Baron Kelvin is an old, ugly, fat psycho and Ciel is a beautiful little 12-year-old. Also, he apparently fell in love with Ciel when he first saw him at age 7, and is keenly aware that Ciel is beautiful while he is not. He becomes determined to get surgery and change his appearance, hoping to "become beautiful" and therefore worthy of Ciel, since he believes that "only special people can touch other special people". He also doesn't care at all when his wife divorces him because of her disgust towards his unsavory actions. Ciel himself confirms it in chapter 31
The Undertaker seems to have some Ho Yay towards Ciel. It's especially notable in episode 6 when he is seen watching Ciel at Angelina's funeral from a distance and approaches him after the funeral is over. He calls Ciel kind for giving the last victim of the murders a grave, while caressing/poking Ciel's face with one of his long fingernails, and leans in close to Ciel when questioning if he regrets not making saving her life a priority. Ciel mentions something about "Queen Victoria's distress being lifted" and the Undertaker replies that he doesn't like Victoria since "she just watches from high above and leaves all the difficult matters to you." Ciel replies that its been a duty in his family that's been passed down through the generations along with the ring he wears. Undertaker tells Ciel that the ring is like a collar that connects Ciel to the Queen like a chain called duty while leaning in even closer to Ciel. Ciel shoves the Undertaker away a bit before he grabs Ciel by his tie and pulls him really close to his own body. He then tells him that he hopes the "collar" he wears for Queen Victoria doesn't take his head off one day and releases him. He then turns around and as he leaves, he tells Ciel and Sebastian they can stop by to see him at his shop since he'll welcome them any time.
The Undertaker/Ciel subtext becomes even more obvious in the Campania Arc: In chapter 61, Undertaker grabs Ciel to threaten Sebastian and gets pretty close to him. Chapter 64 has its moments as well: First, Undertaker attempts to kill Sebastian because he is making Ciel "miserable" and later is not very much concerned about the fact Ciel has gotten hold of his "treasure" when he leaves. Undertaker even gives Ciel a surprisingly warm, loving look.
And in chapter 65 Sebastian states that Undertaker does not seem to want to cause Ciel any harm.
Ciel has shown to be more attractive whenever he smiles rather than when he's frowning. This is to the point where Joker in the manga gives him the stage name of Smile in an ironic sense... but then he finds out that Ciel is a damn knockout.
When Alois first meets the mysterious stranger later revealed to be Sebastian he leans into him and smells him before saying he "smells good".
All the subtext between Sebastian and Claude in episode 6.
Some comedic Ho Yay could be argued for the scene in which the Viscount Druitt flirts with a cross-dressing Ciel.
He does it again in Ciel In Wonderland.
In chapter 52 the Viscount Druitt practically flirts with a disguised Ciel, gets close to his face and tells him "I surely wouldn't forget such a beautiful boy such as yourself. I'm looking forward to staring at both your eyes."
In episode 1 of the second season the Viscount Druitt refers to Alois: "Oh, what a grievous mistake God has made! How could such unsullied beauty dwell in the flesh of a young boy?! But I will forgive you, God! Amen."
And he also wears a look of great sympathy upon hearing Alois's sob-story.
In the Hamlet OVA, Lau actually gets a bit too intimate with a cross-dressing Undertaker.
In the second musical, Alan and Eric are really close for 'best friends.'
Doesn't Sebastian say he finds Ash more attractive than Angela?
Ciel taking in Snake, despite lying to him that he was looking for his friends when said friends had attempted to ambush Ciel's mansion and were killed by Ciel's staff. However in later chapters, it's shown that Ciel does geniunely care for Snake, such as the brief encouragement he gives to Snake when other people were mocking his appearance. Also, he told Snake to get on the rescue boats in his place.
There is some rather blatant Foe Yay between Sebastian and Ronald, like in chapter 64 where Sebastian gets really close to Ronald's face.
In regards to the girls Grell Sutcliffe a M to F Transsexual Shinigami initially fell in love with Madame Red before she killed her and once commented that she thought Hannah (in the second season of the anime) had a cute/pretty face.
In the manga, it turns out Les Yay does in fact exist amidst the sea of Ho Yay; many fans aren't exactly sure if The Fashionista Nina Hopkins just has a thing for Mei Rin and kids of both genders, or if she's openly lesbian.
It's easier to go with the latter when you see bothof these sort of things.