The major plot hook is the return of Momma Oyama from an overseas business trip. Reviewers noted the tension of Mahiro’s "identity exposure" crisis, as his mother still addresses him as "kun".
While maintaining its signature "cute girls doing cute things" vibe, the volume is praised for showing characters moving forward—specifically Kaede preparing for university entrance exams .
Japanese reviewers on Amazon Japan specifically recommended the volume for its "generous amount" of tankōbon-exclusive bonus chapters not found in the original serialization. 📦 Special Edition Features Oniichan Wa Oshimai! 9 [Special Edition] - Playasia
Critics and fans enjoyed the introduction of Aoi-chan , the class president, who adds a "fujoshi" (boy's love fan) dynamic that complicates the social circle.