The basic idea behind the alliance is shinki rights along with stockpiling a pool of shared resources. Shinki can serve as many gods as they wish, gods aren't permitted to seriously mistreat their shinki. There's also support with helping each other care for their shinki. I'm still working out the details but that's the general gist of it.

I could see Ayumu talking to him about it, at least! She's always open to allies, whether they join or not.