Shigemaru (繁丸) is a mountain bandit from the "In the Forest, Under Cherries in Full Bloom" adaptation. He survives by hunting wild animals and robbing travelers, living in a secluded mountain hut with his seven wives. He harbors a deep conviction that cherry blossom trees hold the power to drive people mad. During a robbery, Shigemaru encounters and abducts the beautiful Mitsuki, making her his eighth wife. Influenced by Mitsuki, he complies with her demand to kill his other seven wives, pushing them off a cliff. When Mitsuki desires to live in the capital, Shigemaru relocates with her. There, he murders the emperor and usurps the throne.

As emperor, Shigemaru continues to indulge Mitsuki's increasingly violent whims, including beheading citizens who displease her. The oppressive atmosphere of the capital and Mitsuki's tyranny intensify his preexisting dread of cherry blossoms. This pressure rapidly deteriorates his mental state, culminating in intense paranoia and madness. He eventually flees the capital with Mitsuki, returning to the mountains. In a final act, he kills Mitsuki and wanders alone into a cherry blossom forest. His fate remains unresolved, heavily implied to end in death beneath the feared trees. Shigemaru's journey traces a descent from a self-assured bandit to a mentally broken figure, illustrating themes of obsession, manipulation, and psychological collapse.