Last year I started reading the Spice & Wolf series by Isuna Hasekura. It's what is called in Japan a "light novel" series. It's a short novel comes with a few illustrations up front and more or less makes for "light" reading, though I'm a little skeptical about whether that's where the name comes from.
Light novels appear to work much like comics in that they are serials marked by volume number rather than with a separate title for each installment. If Spice and Wolf is anything to judge by, each volume is a self-contained story, an episode if you will, of the larger series, with an overarching storyline running between multiple books.
It's not quite the same as a fantasy trilogy, which is why the serial analogy works.
For instance, in volume 1 of Spice and Wolf, the characters of Lawrence and Holo begin traveling together, with the goal of returning Holo to her long forgotten home in the distant north. That's the overarching story. But the climax of volume 1 has nothing to do with her homeland, so much as to what lengths do Lawrence and Holo want to remain traveling companions when they have the opportunity to part ways.
Volume 2 covers a deal gone wrong where Holo has to bail Lawrence out of a mess of his own creation, which of course is at a city that's a stopover on their travel north.
Volume 3 looks to further the relationship between Lawrence and Holo as their journey continues (since there's definitely some unresolved sexual tension between the both of them), with of course another wrench thrown in the plan.
Persumably the series, which has gone up to sixteen volumes as of this writing, continues in this way until Lawrence and Holo inevitably find Yoitsu. Or, perhaps, there will be a different reason for them to keep traveling.
Spice and Wolf is a fresh and breezy read. It's a very minimalist sort of narration with short paragraphs, lots of dialogue, and the pages turn fast.
I don't think we really have an analog to the light novel in the US, save the ones that are translated from the Japanese, and that's too bad. I feel like we're missing some sort of marketing niche.