Your Kira reminds me of my boy Yoghurt. I adopted two babies last summer and it took him a few weeks to warm up to them while his brother took to them like a fish in water. Almost a year later and Yoghurt still occasionally hisses and swats at them. My theory is they're the babies now and he's salty about not being the baby anymore. He's younger than his littermate Mango, and though probably not by more than a few minutes, I think he's milked it for all it's worth XD