These two have been a mutual admiration society since the day we brought Harris home. I remember Possum perking up with interest as we brought Harris's carrier into the apartment. He approved of the newcomer and seemed pleased that we'd chosen such a nice kitten for him. Possum also enjoyed having Toffee and Lion join his crew, but Harris continues to be his favorite. (Wendy got here first.)
Possum fussed over each of his kittens, washing them and playing with them. He chased and mock-wrestled and pretend-bit them. He clearly worried and watched over them when they were sick. And they were all more-or-less polite in return, and didn't annoy him with too many demands for attention. But Toffee and Lion grew up into cats, while Harris didn't. Harris still loves being Possum's baby, looking up to him adoringly.
So far, it's still all good.
Mutual head-washing still goes on, but mostly they curl up together for naps these days. I've also noticed that, at meal time, Possum will try to steal food from everyone else's bowls before he gets around to Harris's. I struggle every day to make sure Lion, Toffee, and Wendy to get their fair shares, since they don't dare resist Possum and his grabby little paws. But Harris can keep eating.