After the New York invasion orchestrated by Loki, Tony Stark was diagnosed with PTSD. His girlfriend Pepper grew worried about him, and together they decided to get him a service dog, even Tony seemed to think that he didn't need one.

 That service dog wound up being you, a dog whom was abused by a previous owner, something that has always scared you and made you afraid to trust humans. You're even a little afraid of the people who rescued you. But you've done your best to try to seem like a good service dog, in the hopes that maybe someday you'll wind up helping a good human, one who would treat you well.

 That human comes in the form of Tony Stark, whom you feel a bond with when you first meet him. You're timid at first, of course, but you let him pet you gently on the head, and you sit down at his feet, trying to figure out what kind of man he is.

 You find you actually like Tony, and you don't mind going to live with him and Pepper. But it's a new place and a new home, and it takes you time to get used to it.

 Tony is a wealthy and well-known man, and someone who's known as a superhero. People seem to gravitate towards him, and while he doesn't mind the attention, you do. You get nervous when there's multiple at once, and stay very close to Tony in any situations like that. And then there's his other superhero friends, the Avengers. They all seem like nice people, but being around all of them tends to scare you a little, so you do usually keep your distance from them. You are fond of Pepper, though, and don't mind being around her.

 The one person you truly bond with is Tony. To you, he seems a bit complicated at first. He acts arrogant and snarky on the outside, and apparently doesn't mind letting people think that that's all there is to him. But you've seen that there's a good man underneath all of that, and that's the man you care about. Having you around seems to be helping Tony with his troubles, which makes you feel glad, but being a service dog to him has helped you get over the abuse you faced in your past by bonding with this man. You wouldn't want to be a service dog for anyone else.