Backstory! Perhaps, in asking oneself whether the payoff is worth wading through four volumes of sometimes-good and oftentimes-droll, middling character drama, one loses sight of the reason for such rhetorical compunctions. HIGEHIRO v4 paves the way for a neat and tidy conclusion, but ultimately refuses to grant its characters the resolutions they have purportedly earned. Yoshida and Sayu, confronted by the past, seek to validate whatever meager depths their relationship has forged; they pledge to do well by one another, acknowledging, in part or in whole, they're proud of one another.
HIGEHIRO v4 isn't a particularly compelling volume, and the backstory it reveals about Sayu's past, as well as the reasons for her running away from home, isn't particularly compelling either. One could blame the author's preposterous delay in offering the reveal (four volumes is long time to go without such details), but that wouldn't be quite right. One could also blame the conventional nature of the reveal (survivor's guilt is entirely too common), but that might also sell the author a bit short. In the end, the current book is a fair representation of the whole novel series: clever and well-meaning without being too sharp, too poignant, or too original.
Sayu's older brother, Issa Ogiwara, the first son of a food packaging and distribution magnate, tracks down the duo and pleads to bring the girl home. All manner of odd dynamics ensue, the most pressing of which is that Issa isn't as arrogant and hard-hearted as readers were initially meant to believe. Issa and Yoshida get along quite well, and when the two men agree to give Sayu one week to say all of her goodbyes, the two adults concede it's time they grew up a little as well.
The novel's interweaving of Sayu's sorrow with Issa's culpability with their (divorced) parents' emotional dislocation is a relatable but unoriginal dynamic. Family issues. School bullying. Domestic violence. Parental negligence. These facets are not made less important for their commonness; rather, their overly simplistic summation in the novel series' fourth volume means readers will be less inclined to sympathize with the Ogiwara children, now, than they would had they read about these crushing physical and emotional detriments back at the story's beginning. HIGEHIRO v4, it turns out, needled readers' curiosity for a bit too long. One no longer feels as invested in learning (and acting upon) the truth now that it's finally emerged.
Yoshida's world-class dithering means he'll embark on one more journey to ensure Saya returns home safe and sound. Readers can likely anticipate another confrontation or two in the near future, but at this point, the man's peaceable nature likely won't produce much more than a stern, awkward conversation and a teary-eyed goodbye.