Breadth-First Search for Six Degrees of Separation in mongodb

I have a video-game themed Six Degrees of Separation app and I want to know the best way to implement breadth-first search using node.js and MongoDB.

My app uses https://github.com/mongodb/node-mongodb-native for MongoDB.

For the collection that I'm using, my documents look like this:

{
  _id: "Mega Man",
  with: [
          { _id: "Wolverine", in: "Marvel vs. Capcom"},
          { _id: "Snake Man", in: "Mega Man's Soccer"}
        ]
}

If I want the characters related to Mega Man, I'd need a query to produce

[
  { _id: "Wolverine", with: [...]},
  { _id: "Snake Man", with: [...]}
]

So:

1. What query/queries would I use to get a list of characters, each one with an _id corresponding to the _ids in the with field of any given character?

2. How would I query the database if I want to get all the characters that are n steps away from a given node?