They're on my list of future snakes, so it's good to hear that they're one of the more mellow species.
From anecdotes online, it seems that Japanese rat snakes are flighty when young (which makes sense) and become a lot more mellow with age and handling. I know not to judge her attitude towards handling based off a single care in my care; she did just get hauled to an expo, displayed for hundreds of people, and then ferried home with two Big Warm Predators who May Or May Not eat her.
Even so, she's already incredibly curious, and is constantly watching me as she moves around her enclosure. A lot different than a ball python, that's for sure.