In some ways, Josh is kind of the 'wise mentor' when it comes to Aather, in that he was one of the few people still around from Joy's introduction (the other being Kitsunebi, whose age and general inexperience with humans makes it hard to for Joy to consider him a mentor). It's a bit more even both as Joy recovers more memories* and gains direct experience with Aather.

Sell me on Josh's canon?

* The seasonal countries really gives Joy ideas about Aather.