DISCLAIMER: this fabulous anime/manga ain't mine, boys, girls , transgenders and aliens. also MASSIVE SPOILERS. I RECOMMEND FOR YOU TO WATCH/READ THIS AMAZING ANIME/MANGA.
Ciel and his brother, Astre, were always together. They played, slept, and talked about everything together. Astre was the weaker and younger one, while Ciel was the more strong and first one. Ciel and Astre were so close, they would not need to communicate with anyone else.
oh, how Ciel loved having his brother near. Ciel felt safe, and at home with his brother. his most favourite way of keeping him close was hugging. the feeling of his brother's soft body pressed against his was refreshing. sweet woodburn and chocolate was his scent.
so, when Astre told him that he wanted to leave to london and open a toy shop. Ciel's heart very nearly stopped in his chest. He thought, "why would he want to leave me? if i am attached to astre on such a deep level, doesn't he feel the same?". when Astre tried to comfort him by saying that he and Elizabeth would be together forever, he frowned. yes, his fiancee was a very lovely girl, but his heart was Astre's. not his father's, not his mother's, not Tanaka's, not Aunt Angelina's, and certainly not Elizabeth's. his heart was held by astre's tiny hands that he was grasping ever so tightly.
Rachel and Vincent Phantomhive were worried. Their eldest son was getting more and more attached to his brother, and he was showing no signs of stopping. if anyone tried to separate them, he'd throw a tantrum for sure. after that, he'd drag his brother to thier bedroom, glaring at anyone who tried to stop them.
when Astre had his asthma attacks, Ciel went into hysterics. he tried everything to help his brother. when the incident was over, he'd sneak into Astre's bed and hold him close.
speaking of sleeping and beds, Ciel couldn't sleep without his brother to cling onto. Ciel and Astre often shared a bed. that was until one of the parents tried to pull Ciel away. he'd scream and scream until they let go, and before Astre or either of the parents could blink, he was clinging to Astre again.
when Astre told Ciel about his dream of being a toymaker, he had expected for Ciel to be happy. but, when he saw his brother nearly cry and ask him why did he want to leave him, he was confused. he tried to comfort him by telling about Elizabeth, but he just frowned and pulled him into a hug.
when that fateful day came, and they were thrown in a cage, it was Astre's turn to comfort Ciel. Ciel could do nothing but cry silently as Astre held him and whispered sweet nothings into his ear. when he was taken away, he could do nothing but cry, as he and his brother were no longer together. He thought of Astre as he died.
when undertaker revived him, all he could think of was Astre. his brother was shocked to see him. he was so proud to see Astre all grown up, but also in need of protection. but he wasn't pleased about, was that demon standing between them. how dare that vile thing think he is worthy of his brother!
when he was in Astre's head, he offered for him to stay there forever. no demons, no adults, no strangers, no society to break them apart, no birth rights, just them, together forever. when he hugged his brother, he was pleased to note that Astre still smelt like woodburn and chocolate. so, of course he was devastated when he left.
he followed ciel around as an invisible spirit and was angry that he trusted strangers. especially " Soma". he was angry and felt replaced when Soma called astre " little brother". he tried to kill soma out of jealousy, but ended up killing Agni. he left the note "who stole the candy from mu tummy" to his brother's room as his way of saying, i'm coming for you.
now they were hugging. in their bedroom. Ciel was pleased to note that his brother felt like home.
yet he was trembling violently. Perhaps from the scary story he told? until his brother asked "why?"
he was confused. then it cleared. his brother meant those "friends" he killed to keep astre away from harm
so he told him " i destroyed them because they only meant harm" he looked at his brother's shining blue eyes.
" they tried to take you away from me" he continued, leaning close to astre's ear.
"they were foolish, though. for they didn't believe that you are still mine"