It's definitely sf, but it has a fantasy feel because the action is entirely on a feudal planet that hasn't seen much social change since the coming of interstellar trade. It's a nice demonstration of "sufficiently advanced technology is indistinguishable from magic" - Ren is from a high tech culture and given a few hours or days can work out how the Imaiz does things like causing an explosion in a locked warehouse, but the locals have no hope of doing so; not because they're stupid, because they aren't, but because they don't have the base level of experience with technology.