This novel is about friendships: those that are positive and lasting and those that are weak and break down.
The Divine Wind is about friends and relationships mostly, but other issues are raised as well. .
In the book none of the friendships/relationships are totally positive and lasting - they all go through weak spots, but it's only the true friendships that begin again or survive. It's more about strong and weak friendships.
Hart and Mitsy's relationship proves this. It was the main theme of the novel (so it was gone through in a lot of detail). Hart says friendship is a slippery notion. We lose friends as we change and our friends don't, or as we form other alliances, or we betray friends or we ourselves are betrayed (21). All these things happen between Hart and Mitsy and yet their friendship endures, eventually. First there's the incident with derby - where Mitsy sees Harts reaction as a betrayal. Also the Japanese side of Mitsy is a different allegiance - as Mitsy sides with her family and Hart with his. Then Harts perception of Mitsy changes; "They seemed to undergo a kind of shape shifting. It was as if they"d been caught in the tricky variable light and shadow of a candle - only the alteration was permanent - not momentary." That was the biggest break in their friendship as well as the cultural differences - it all comes back to that. Alice's official letter is just the breaking point. When Mitsy leaves they part as friends, but if they weren't true friends why would she have written the letter hoping to become closer again? .
Jamie and Hart are not good friends; they were just thrown together as they were in the same place at the same time. They did not choose to be friends because they liked each other - but simply out of circumstance. Jamie was very competitive so the friendship could never be equal, it would only ever last until one broke. "WE often make friends for the weakest of reasons - proximity, for example, or shared experience or laziness or need - but what makes them endure as friends? Their similarity to us? Their utter difference to us? (21).