The impression the novel gives is one about coping mechanisms after hitting absolute lows. The characters grapple with their trauma and become so pathetic it evokes almost disgust. The emotional context that is absent or implied in the anime is actually properly explained here, making it more enjoyable. Circumstances are introduced and reintroduced- quite explicitly, in case you forget. The common thread of characters is dealing with loss, guilt, or both. It's a story that starts so low you wonder how they can heal, and ends on a hopeful note.
However, the development is quite casual and serendipitous, accelerates to break-neck pace at the climax, and concludes with the feeling of a precarious happiness. The simplistic "fun things are good things" takeaway, the deterministic outlook of the tanuki, and message to accept the ephemerality of good times seems to me stereotypically Japanese and stale.
In addition, despite the character of Benten and her trauma, a different kind of trauma, being the primary drivers of the conflict, the mystery she casts looms over the rest of the novel. As the first book in what is a planned trilogy, it is understandable, but a little frustrating for this novel to serve in large part as a prequel to her story. With the way the titular heroes' stories are resolved, they become like minor characters to their own debut novel. Although in-theme with the tanuki nature, I found it a somewhat depressing affirmation of the things being the way they are.