There are times when Ianto finds himself wondering whether he’s an extension of his TARDIS or if she’s an extension of him. In the end he supposes it doesn’t really matter; right from the moment she found him in the void and grew around him to save his life they’ve been so inextricably linked it’s difficult to be sure where one ends and the other begins.
Physically they’re two separate beings, one mostly human and the other organic technology; each of them is perfectly capable of existing independently of the other in that respect, but their consciousnesses are woven together like an intricate tapestry, the threads of their two minds impossible to separate.
Long ago, when his mind had briefly been linked to Gwen’s following a slight accident with alien technology, Ianto had found the experience deeply disturbing. To be privy to another person’s thoughts and memories had felt like an invasion of privacy, and he’d learned far more about his colleague than he’d ever wanted to know. Uncomfortable though it had felt being unable to act of his own free will and consequently forced to copy everything Gwen did, it had been less of a trial than having his mind swamped by her thoughts and emotions.
This, with his TARDIS, is completely different; she doesn’t control him, and he only has limited control over her. She’s still her own person, even though she willingly accedes to his wishes, taking him wherever he wants to go and providing him with whatever he needs, be it a specially constructed room within her walls or the correct currency for whatever world they’re visiting.
She’s a passenger within his mind, no matter what he’s doing, an often silent but always comforting presence, instructing him when necessary but in no way distracting him when he needs to concentrate. Because of that she doesn’t feel at all intrusive, so he never wishes she weren’t there.
Even before they found Jack, when Ianto died he revived knowing he wasn’t alone, feeling her concern like a reassuring embrace, washing away any lingering weakness and pain, and leaving him ready to deal with whatever situation he happened to be in. She’s his companion as much as he is hers, more like different aspects of the same person than two separate entities.
Now that Jack has joined them, they’ve become a triad of sorts, three persons joined at the soul. Through the TARDIS, Ianto has discovered he and Jack can exchange thoughts over a considerable distance. Even when they’re apart for whatever reason they can reach out to each other, communicating through emotion as well as thought, and sometimes they can even see through each other’s eyes. It’s a strange sensation but not unpleasant.
He and Jack understand each other far better now than they used to, which is mostly a good thing. They don’t get their wires crossed as often, and when they do the TARDIS sets them both straight. It makes for fewer arguments and less sulking, although Jack can still pout better and more effectively than anyone over the age of seven should be able to. Ianto still finds it infuriatingly cute but he can no longer pretend he doesn’t; the connection the three of them share does have a few downsides, but they seem insignificant when weighed against the benefits.
They can’t lose each other; wherever any of them happens to be the others can locate and rescue them if needs be, and they never have to be alone unless they want to be.
When it comes right down to it, maybe they’re less extensions of each other and more of a fusion, three living components that fit together seamlessly to form something greater than any of them could be on their own.
Ianto can scarcely remember what it felt like to be the way he was before, when he was nothing more than an ordinary mortal man. So much has changed. He thinks it’s for the best, even though he can’t go home and visit his family. He misses them; probably always will, but Jack and the TARDIS are his family now. Maybe someday they’ll have children of their own but there’s no rush, there’s more than enough going on to keep them busy. All of time and space is spread out ahead of them and they’ve got a lot of exploring still to do.