The Trails books are relevant to story things generally. Almost every Trails book, at least prior to 3, is related somehow to story things or likely will relate to story things in the future. For example, the first book in the series, Carnelia, introduces both Toval and his partner Ein, well before they're actually both important. CS1 is the first time we've seen Toval in person, but he was introduced in the first book series we have. Red Moon Rose, this games book, also happens to be incredibly important.