Dear Internet: This may have a lot of canonical errors. This may ruin canon characters, or change their backstory a little. Don't get your panties in a bunch, you'll get nothing from flaming me. I do, however, like nice little, polite notes letting me know if I do something good or bad. You've been warned, at some point in the future this will likely involve dudes getting it on.
On with the show.
It was hard to keep track of his names, he tended to respond to at least two, and to think of himself without the importance of one. Yoko called him "Alucard" in private, "Genya Arikado" to outsiders, to Soma. His true name he kept to himself, he had never told anyone, and no one still living knew. The name had never really seemed right, coming off the lips of others.
He had wanted to share it, once, so long ago, beautiful Maria. If she had followed, he would have given it to her, shared his name and his life, who he was and who he had been. But she had left him to his own mind, to his hiding, likely for the best. A human would have drawn things near that would have him abuse his power, fulfill his bloodline and his potential. At least this way Maria had been protected, from anything besides the passage of time. Agelessness was a punishment, he had discovered. Every time he had awoken, he was forced to know how many years, decades, then centuries it had been since she had died. Since he had last wanted to share any of his life with anyone.
Yoko had urged him to stay away from the castle this time. She couldn't hear the voices calling him to it, the threats to Soma, the power it had gained from that other world. They wanted Soma, this time, so sure that he was going to give his body over to the power that he carried the ability to wield. Yoko could not keep him from the castle, only follow and hope to save one of them. At least he knew she would save Soma, he was the one that needed the help more, he hadn't lived in this castle, ever changing though it was, some things were always there. He knew this place, he knew some of the inhabitants, though some had not passed the test of time.
Humans stood out in this place by their scent alone. Yoko could disguise it, but Soma was too easy to track. The boy was fending off creatures that the castle birthed, the monsters flourished in a place as cursed as this was, and more would come, more and more trying to overtake the boy and steal him away to resurrect their master. He reached for a sword only to remind himself he had none, he couldn't take his real form around Soma. The boy likely didn't even know that he could fight. A monster's rusted sword clattered to his feet, and he grabbed it, instinct, to fend off the creatures until they got some kind of idea what was going on and ran. The battle crept him closer and closer to Soma, he could see the determination in the boy's face- he was convinced that this was right, what he had to be doing. He had to admire the boy for that.
Finally, they stopped coming, the room was empty. They were barely inside, a long hallway stretched out leading into the castle proper. Soma looked up at him, his eyes wide.
"Arikado," He was perplexed, "what're you doing here?"
"Helping." He tried to keep his words short.
"Well, thanks, I guess."
He nodded, looking around the boy rather than at him directly. He could rarely meet people's eyes, they would start to see, start to get an idea that he was not entirely like them, not entirely human. Besides, Soma was beautiful, something he had failed to notice before. People had changed, even in the eras he had seen, people had changed, gender lines blurred, he realized that it wasn't that big a deal to him if it was a boy or a girl. But this was a recent development, the last time he had been working in the real world he could have been hanged for finding a boy, even one so effeminate as Soma, beautiful.
"Are you going to come with me this time?"
"I suppose, if you would like for me to."
"I would." Soma smiled for him.
They explored the halls together. As much as the castle changed with every incarnation, so much of it stayed the same. He had grown up in this place, after his mother had been killed, wandering these halls and trying to avoid the things that served his father. Sometimes he would see a room and know just where to hide, a secret wall or floor panels that were loosed. Soma didn't know these things, and he didn't want him to. He kept to himself, a great deal of the time, kept secrets.
"I didn't know you could fight, Arikado."
"I've never had to."
"But still. Its useful."
"It can be." He wiped the blade he had stolen from a monster on a long coat, and looked at Soma. He was touching up his own wounds, catching his breath. The room seemed empty, it was cold, hardly lit at all, even more so than the rest of the castle. He could see Soma's breath. Death was near.