Ratchet wasn't fond of humans, that much was clear. Despite being fond of raff, Miko and jack he disliked most humans.

The aren't great, he'd like to call them downright crazy and blood thirsty but he couldn't speak much when the entire reason he was on earth was because Megatron was crazy and bloodthirsty.

Albeit Megatron is also traumatized, so maybe humans were deranged because of trauma as well.

Either way, he kept his distance from most of them. Both to prevent a situation where humans try to hunt them down and because he just didn't like them.

But then you stumbled upon him while he was stopped in a parking lot, it was late and he didn't realize that you were there until he transformed and heard a gasp.

And now he's grouchily organizing his medical supplies with you on his shoulders. Optimus decided that he'd be your guardian, so you spent a good portion of your time at base with him.

Despite himself, ratchet had grown quite fond of you as well. You were quiet and didn't disrupt him very much. Plus, you showed some curiousity in cybertronian medical procedures so you couldn't be all that bad.