Some ramblings:
I think shadow would become obsessed with reading about Mobians and specifically hedgehog cultures, the more time he spends with sonic.
He's made of 3 parts, human, hedgehog, Blackarms. I'm sure he'd have enough of his alien blood and he was raised by humans, they're all around him... But his curiousity with Mobius might be interesting, given they're not from earth. Surely he wants to know more.
Shadow feels like he'd be someone that needs a reason to do something, resulting in him becoming stressed and bored when everyone else is just chillin'... but he also feels like someone who'd be stuck in his thoughts at times, pondering things to an unhealthy degree.
When he lands on something, he sets a goal to find whatever it is he wants to find and will get tunnel vision, obsessively researching until the goal is complete... Being unable to complete things would not be an option to him.
Unless someone can break him out of it, he'll run himself dry lol. I think he'd do this with sonic, wanting to understand small aspects of Mobian culture, wondering how the history of the culture shaped sonic, or if sonic is really an outlier. An outcast that happened to work, despite it all.
Sonic hides much of his life from everyone. Even tails isnt always sure what's happening in his head, only knowing what he experienced with sonic. He doesn't know what Sonic doesn't tell him. No one does, no one but sonic.
Funny enough, this would be a huge issue between them, as Shadow works to open his heart, he wonders if Sonic's is as open as he says it is...














