I'd love to be the love interest, as the MC is super nice and would be a great partner, but I don't really like guys, plus I based some of his personality off of me and that'd be weird.
I wouldn't really want to be an animal, being a human is way cooler. But also the MC's pet kinda dies so yeah, I don't wanna be them.
There are already way too many supporting characters, don't want to add another to the crowd.
Isn't the antagonist's foe just the protagonist? I guess that could work.
Honestly I'm already a couch potato, so that'd be pretty boring. I'd want to actually do something in that story, since the world is so cool!
If I were some random passerby, I'd probably either die in a large conflict, or have an extremely boring life. I do intend to add in my sona to the background crowds, though.
So I pick MC's friend, since that seems like the best option.