Sometimes, when she thinks that he isn't looking, Valkyrie changes her walk from an imitation of his straight-backed march to a smooth, fluid lioness’s stalk. He has only seen one other person with that one particular walk before in his long, long life, and she's dead or dying.
Valkyrie and Darquesse are abnormalities, he thinks to himself on the long car drives to isolated crime scenes. Before Darquesse had became independent, he couldn't truly tell the difference, where Darquesse’s bloodthirst ended and where Valkyrie’s anger began. If he didn't know better, he would compare their situation to himself and Lord Vile, but he thinks that that comparison that would be a dishonor to Valkyrie.
Skulduggery Pleasant knows that Valkyrie Cain misses Darquesse. Death had never affected his observational skills, only his emotions. Valkyrie attempts to cope with the loss of (the parasite? her other half? herself?) in subtle ways. She's picked up an interest in magic theory and disciplines of magic, and sometimes takes a bit too much delight in violence then is strictly necessary. Sometimes, she goes dead-quiet and grasps into his arm, staring at his feet.
He doesn't really know what to think of that, so he pushes away his discomfort at how intensely she looks at him when she gets like that and leads her forward until she lets go.
If Ghastly was still alive, he'd most likely pull Skulduggery off to the side and ask him just why his apprentice was becoming so violent and dependent on him. Ghastly wouldn't, hadn't, said it out loud, but Skulduggery knew that he was worried about Skulduggery influencing her too much. Deep down, he agreed with Ghastly’s concerns. Deeper down, he was glad that there was someone else like him and someone that needed him. So Skulduggery Pleasant doesn't intervene, doesn't ask Valkyrie why she's acting like this, why sometimes she gets this look in her eye that she knows too much, why sometimes (more often now) she seems inhuman.
Valkyrie Cain knows that something is wrong with her. She misses Darquesse, and she knows that she shouldn't, but there is something that is profoundly wrong with having a gaping hole where (a monster? a goddess? a sentient ball of all of Valkyrie’s power and wishes?) had once resided. Most days, it's not hard to ignore the void in her chest, the lack of another being that understood her perfectly. Some days, it's not. On days like those, she imagines Darquesse’s voice whispering in the back of her mind (for all that she knows, it’s actually her and their connection still exists between dimensions).
Sometimes, the world around her turns to a shining, sparkling web of magic and electromagnetic impulses when she wants it to. Most of the time, the change from her normal vision to this indiscernible whirlwind of colors is abrupt and unintentional. She knows that Skulduggery has noticed by now, how sometimes she goes quiet and presses closer to him than she usually does (she can only recognise him because of the enchantments that lay over his bones) until her eyes stop burning and she can see again. Valkyrie knows that he doesn't know why, and she wants to tell him. But.
It seems very intimate, being able to see a person’s magic, and she knows that Skulduggery isn't truly comfortable with intimacy. So she doesn't, and stays behind her (best friend/hero/teacher/refuge/solace) and bites back the feeling that she could be more, that she could do better than this. Because she has done better, she has became more and that resulted in hundreds of people getting killed. For now, she is content with solving mysteries and crimes with a dead man, content with swallowing the bile of you could be a predator.
Tanith Low is well-acquainted with both Skulduggery Pleasant and Valkyrie Cain. She knows that the two of them are far too codependent for their own good, and she doesn't know what to do about that. Something tells her that neither one would be too happy being forced to acknowledge the truth. So Tanith doesn't bring up how Skulduggery watches Valkyrie when she's away from him, how Valkyrie leans into his touch. How when one falls, the other doesn't stop until they are safe.
One time, shortly after Darquesse had been banished, she had asked Valkyrie about just how far their relationship went as a joke. Valkyrie had left, and as she closed the door behind her, Tanith could see the deadly white sparks dancing across the doorknob. They didn't talk again for three weeks.
Tanith talks to China sometimes, while Valkyrie and Skulduggery are researching in the Grand Mage’s library. The conversation usually turns to Valkyrie Cain and the question of “What comes next?”
Neither woman knows. But China says that Skulduggery and Valkyrie’s relationship is probably the best option now despite how unhealthy it is for both of her friends, and Tanith reluctantly agrees. The two of them temper each other. Valkyrie Cain is the only one who is able to predict and calm the Skeleton Detective’s moods (China says that aforementioned moods happen because of a mixture of his trauma and the magic holding his bones together), and Skulduggery Pleasant is the only one able to pacify the Last of the Ancient when her gaze is uncomfortably close to a vampire’s starving stare (the Ancients weren't completely human, China explains over an ivory cup of tea). Together, the two of them are almost functional. Apart, people tend to die. So Tanith doesn't say anything to Valkyrie, simply offering reassurance when Skulduggery has a bad day, and tries to distance Valkyrie from Skulduggery when Valkyrie puts her head ever-so-slightly down and her pupils gloss over with a dim glow and she stares through (at?) Skulduggery’s well-polished shoes and only responds to his movements and sound.
China Sorrows knows exactly what is going on. She knows the enchantments animating Skulduggery’s bones, she has read all about the Ancients and their magics.
When Skulduggery is stiller than he normally is, China Sorrows subtlety gets in his way and alters the magics around his skull that are wearing away. The next day, he's back to normal. China knows that animated objects aren't supposed to be animate for over three hundred years, but Skulduggery (as always) is an exception. After the Skeleton Detective discovered the truth about her involvement in the deaths of his family, he drew away, colder than she had ever seen him.
It's his enchantments, she knows. When he was alive, he couldn't be coldly furious in the way he was now infamous for. China is one of the most knowledgeable Adepts of the world, and one of at most three people that knows just how Skulduggery works, how he's able to think and move and feel. It’s nothing like how he used to think and move and feel when he was alive. Sometimes China mourns who he used to be. She shouldn’t, of course, seeing how all of this was her fault, and yet...
China Sorrows knows just as much about Valkyrie Cain as she does about her mentor. History has always been (spotty? evasive?) about Ancients, and all China has to learn about Valkyrie and her heritage are documents hundreds of years older than she is and stories she had been told as a child. So China does her duty, and records the evolution of Valkyrie Cain’s powers and compares her magic to the Ancient descendants of history.
Valkyrie Cain’s powers now are exactly what the others had been, and that concerns China. One of the many things her upbringing as a devotee of the Faceless Ones had been useful for was a rich oral history of the past. One of her brother’s favorite stories was that of the Ancient’s treachery. As China remembers, it's a short story, but it talks of the Ancients as not just a sect of worshippers of the Faceless Ones but as the children of their greatest devotees and the Faceless Ones themselves (China purposefully doesn’t think about how the union must have happened).
China knows that Valkyrie is less human than her partner. Skulduggery is still human bones and magic, but Valkyrie is magic and human and something else. It’s hard to see unless if a patient observer is looking for subtleties, but China is patient, observant, and perhaps a little bit too invested in Skulduggery’s partner. As the years go on, sometimes China can see Valkyrie’s thin facade of humanity waver and something far more primal shine through. Few things truly frighten China, but a lone, enraged Valkyrie and Skulduggery easily make that list.
Skulduggery Pleasant, Valkyrie Cain, Tanith Low, and China Sorrows all know that one day, something is going to go catastrophically wrong. China has made preparations for all of the possibilities that she can think of, but Skulduggery Pleasant and Valkyrie Cain have always been eerily good at walking into unexpected scenarios. Codependency ends quickly, and codependency ends messily. All that they can do is wait, and try to stave off the inevitable as long as possible.