The romance amidst the destruction will be appealing to readers. Mio's inexplicable connection to Shinobu is not treated lightly, and we do learn why it is such a compelling force in her life. There is an interesting interchange between Jack and Hikaru-- in his human for, the kitsune puts the moves on Jack, only to find out that she prefers women. This is not a problem for a shapeshifter, and Hikaru changes to a female form. The explanation of gender fluidity is matter-of-fact and handled well. There is a brief interlude when Mio and Shinobu share a moment that ends with Mio acquiring some grass stains, but there is nothing instructional that would prevent this from being appropriate for middle grade readers.
Mio is a strong but conflicted character who doubts her own strength but is ultimately able to summon it against the odds. I appreciated the fact that her parents both play a role in the book, and that she is both protective of them while wanting their approval and protection as well. Rachel gains power after her attack from a supernatural being in a previous book, and helps to save the day. Incidental characters like Mr. Ebisu add depth to both the mythology and the story in a satisfying way-- I want to hang out at Mr. Ebisu's book store!
Frail Human Heart is a brilliantly titled and satisfying conclusion to The Name of the Blade Trilogy that will have fans sighing with relieved contentment and waiting to see what Marriott will write next.