For people who like Yudkowsky's fiction, I recommend reading his story Kindness to Kin. I think it's my favorite of his stories. It's both genuinely moving, and an interesting thought experiment about evolutionary selection pressures and kindness. See also this related tweet thread.
I suspect "friendships" form within the psyche, and are part of how we humans (and various other minds, though maybe not all minds, I'm not sure) cohere into relatively unified beings (after being a chaos of many ~subagents in infancy). Insofar as that's true of a given mind, it may make it a bit easier for kindness to form between it and outside minds, as it will already know some parts of how friendships can be done.
Spoiler block was not supposed to be empty, sorry. It's fixed now. I was using the Markdown spoiler formatting and there was some kind of bug with it I think, I reported it to the LW admins last night. (also fwiw I took the opportunity now to expand on my original spoilered comment more)