Can one's story begin at the end and if so does that make that end a beginning? He never really knew what exactly a beginning was, nor an ending. Just existence. Never ceasing yet never really beginning either. The same stale air of the underworld, the same dull coloured rock walls which even if he tried even Hercules couldn't find a way to knock them down. Castien was always trapped in a sort of....normality. He slept, awoke and served. Nothing more, nothing less. Lived his boring life as his mistress directed him and told him what he needed to do and when she needed it done. To be honest he didn't even delude himself with thoughts of promotions or even being given better jobs. He just served, he served until it broke him.
Castien's story isn't exactly as bland as he makes it out to be, he just prefers to not talk about it. Years of guilt, death and general f*ckery have just made it too confusing for a regular human or demigod to comprehend. Maybe Mnemosyne would understand, maybe if he poured his heart out and asked her to comprehend his inner desires, maybe even she wouldn't be able to interpret them.
I guess Castien's story begins a long time ago when Greece was still home to the Gods and Hecate was being too lazy to create demigod slaves. More people were praying to her and she needed someone to sort things out so alas Castien popped into existence. Then the cycle began, the never ending circle of events. It wasn't until about 1781 when Castien actually begun getting bored with his life. Hecate, with fake compassion, decided to make another servant as Castien's sister. Of course they weren't biologically related but Hecate made them look and function alike in many ways which in turn caused many to call them twins.
Castien enjoyed the company and wondered how he managed to function for the many years before Calaena was created. Life wasn't a dull cycle anymore, still a cycle yes but it wasn't dull. The twins did their duty as Hecate wanted them to, never hesitating to fulfil their orders.
Hecate never revealed why she wanted to two siblings to find a certain man named Thomas Shelby nor did they really care they were used to it, go in, kill the bastard and get out. No reward but at least 'Mother' would be happy. It was the summer of 1919 when Castien met Thomas for the first time and their relationship was needless to say...strange. Both were cold to the other, for different reasons but with pathetically the same result, yet neither of the two were particularly disdainful to the other. Gradually they warmed up to each other, eventually becoming best friends if you will or as close of friends they could get without feeling uncomfortable.
Hecate was growing impatient. Why were the twins taking so long? Calaena wasn't even involved with Thomas anymore, instead she'd taken off to live at camp already and Castien....Castien was actually close to the bastard. Fearing the worst Hecate decided to issue Castien a ultimatum, kill Thomas by Christmas Day or she'll have to do something about it.
Castien couldn't. He'd grown too close to Thomas to betray him, the thought of it made him sick. He decided to ignore Hecate's threats. On Christmas Day 1920 Hecate lost her patience with Castien and took matters into her own hands. Placing a mind-control spell on Castien she had him burn Thomas and his gang's warehouse to the ground and then once Thomas showed his face Castien would shoot him. It went according to plan and Thomas 'died' that night (although later Hecate would learn that Nemesis intervened). Castien's mind-control spell was lifted and he just shut down. How could she have done that? The only person he cared about other than Calaena.
To make matters worse Hecate came to Castien when he was in his room in the Underworld, still ashamed and grieving over what he had done and Hecate, wanting to punish him for disobeying her brought Calaena in with her and killed her in front of Castien. Castien never dared disobey her again.
Castien lived the next one hundred or so years locked in the Underworld, Hecate not trusting him with doing any job outside since the 'incident' as she referred to it as. It was only recently Nemesis offered to take Castien to camp and make sure he doesn't get into trouble since it was so boring in the underworld and that Castien could do good with the air. Hecate, reluctantly, agreed due to having more, even more obedient Lampades to serve her. She didn't exactly need Castien anymore. Nemesis took Castien to camp and well, then Thomas appeared.