That's a good question! The determination to protect, the way he takes his duty seriously - that's something where they mirror each other completely, and they admire that in each other. I also think SW loves how sharp ZYL is, how quickly he sees through things - even when he's holding bigoted opinions at first, that can be remedied by giving him more information and context, mostly. And I don't think what he sees in ZYL can be disentangled from what he saw in Kunlun, the open acceptance he grows into, so that plays a part, too ...

*ponders some more*