Osamu Togashi is a reluctant candidate in the Archfiend Contest vying to succeed the retiring devil king Lucifero. Despite his position, he shows no interest in the competition. Ranked as the weakest among the Archfiend candidates, he left the Infernal Realm for the Mortal Realm, living independently. Having grown up primarily among humans, he possesses almost no knowledge of Infernal Realm customs or typical demon sensibilities.

He works part-time at a convenience store, prioritizing this mundane job over the supernatural conflict and consistently expressing a desire for an ordinary human life. Though participating under duress, he forms pacts with familiars called "Child," entities born from human souls. Physically, he displays cat-like features, including a tail, leading to nicknames like "Rooster Head," and harbors a fear of dogs.

His moral stance emerges through guilt over forming pacts and staunch opposition to sacrificing Childs for the contest, causing him to question his role. His compassionate nature is highlighted when his coworker Yoko transforms into the Child Charlotte to protect him during a battle against the candidate Frej. This act reinforces his reputation for kindness while underscoring the life-or-death stakes he faces.

Despite his perceived weakness, he displays unexpected combat capabilities, often prevailing when directly threatened. His relationships with his Childs are marked by mutual disrespect from some, though his underlying care for them remains evident. Additional facets include undergoing temporary gender transformation during missions, such as infiltrating an all-girls' school, which inadvertently attracts the attention of other characters like Bathory.

His development centers on balancing his mundane human obligations with escalating supernatural conflicts while grappling with the ethical implications of the Archfiend Contest.