I'm watching Onyx gently cleaning Mimi right now - it was something that he did with both kittens, and especially with Loki, all the time. As Mimi got older, she didn't really want Onyx doing it so much, but now, she lets him.
Since Loki has been gone, Mimi's behavior changed - she's become less stand-offish and more affectionate. I think she was a little miffed by Loki's boisterous good nature and overt affection with most people, and stayed more reserved in response. I'd like to think some of Loki has passed into Mimi, and that he is still, in a small way, with us.