SO, in chapter 903 (aka last chapter) we've learned that Koby was the hero that protected the civilians during the Rocky Port Incident. And as the community reminded us, was at Rocky Port that Law got a 100 pirate hearts, in order to become a Shichibukai. Well, looking at it now, I doubt that Law attacked civilians during that incident. It looks like Rocky Port was under pirate attack, this can explain why Koby had to protect people and how Law found that many pirates. And due to backstorys reasons, they both can surpass the Marines vs Pirates rivalry to do the right thing. So, that's my theory! Law and Koby made an alliance during the Rocky Port Incident to defeat the pirates, save the fellow people and, on top of that, Law could become a Shichibukai. We can look at this also as another reason to Law chose Luffy in future. Well, Koby definitely will have a major whole in the story and I think that we'll see he more often during the Reverie. Amazing job, Garp! That weakling become pretty badass.