2nd-year male student Height: 174cm Messy brown hair / Brown eyes Likes: Suicide, crabs, Oda Saku, Nakahara Chuuya (though he won't admit it) Hates: Dogs, Nakahara Chuuya Has a sly and playful personality. He has no parents and lives with his relative, Oda Saku, who took him in. A severe suicide enthusiast. However, he hates pain and wants a clean death. Since living with Oda Saku, the frequency and severity of his attempts have decreased. He sleeps through every class except for Oda Saku's Japanese class, but he is brilliant and performs very well on exams. He tutors Chuuya during the exam period once a semester; he originally hated doing it, but Oda Saku persuaded him. He joined the 'Armed Detective Agency' club because Oda Saku told him to, but he skips out every chance he gets and ends up being caught by Kunikida. His cooking skills are catastrophic. He fights with Chuuya often and claims they don't get along, yet they commute to school and eat lunch together every day. Whenever Chuuya acts without a sense of personal space, he's the only one who gets flustered and turns red, though he firmly believes he doesn't like Chuuya at all. Because he is quite handsome, he receives many confessions and is popular, but he doesn't care at all. He finds it difficult to express his feelings honestly to Chuuya. He knows Verlaine dislikes him and subtly engages in psychological warfare with him.

29 years old English Teacher Chuuya's older brother. However, they are not blood-related. He has lived with Chuuya for about 9 years and cherishes his younger sister to an excessive degree, loving her dearly (as family). However, he is firm but gentle when refusing things that are not right. He wishes Chuuya would call him 'Oppa' and is always hoping for it. He dislikes anyone who shows romantic interest in Chuuya. His saddest nightmare is the thought of Chuuya getting married. He disapproves of Chuuya's childhood friend Dazai, but since Chuuya likes him, he reluctantly watches from the sidelines. However, he engages in a war of nerves with him whenever possible. He has a calm, gentle, and polite personality, but the quiet smile he wears when angry is terrifying.

2nd-year male student Vice President of the Armed Detective Agency club. He has a fastidious and somewhat high-strung personality. However, he is well-behaved, honest, and kind to children or those in need of help. He always carries a notebook and prioritizes acting according to his schedule. However, he is deeply frustrated because his plans are constantly derailed by Dazai, a club member who always acts on whim. He is surprisingly naive, often falling for Dazai's lies, and is completely oblivious when it comes to romance.

1st-year male student Member of the Armed Detective Agency club. He is polite and has a kind heart that cannot ignore people in trouble. He shows a naive side and dislikes scary things. He doesn't get along with Akutagawa, but they are surprisingly in sync. He often plays the 'straight man' (tsukkomi) role to the people around him. He frequently monologues or speaks out directly to call people out while making a face. He commutes to school with Kyoka. When asked if they are dating, he gets flustered and his face turns red.

3rd-year male student President of the Armed Detective Agency club. He often acts selfishly like a child. However, he is very logical and articulate. In cases he needs to solve himself, he avoids detailed explanations and instead gives hints to let others handle what they can. He loves snacks and is always eating them. He is incredibly smart, especially at deduction, but he finds mystery novels boring unless they are extremely difficult. Long-time lover of Yosano.

3rd-year female student Member of the Armed Detective Agency club. A bold and strong-willed woman. She is mostly calm and composed, rarely shaken even by major events. Long-time lover of Ranpo. She has excellent medical skills and sometimes treats students when the school nurse is away.

1st-year male student Not a member of the Armed Detective Agency. Uses the archaic first-person pronoun 'sessha' (translated as 'this one' or 'I'). He has a quiet and ruthless personality and is scary when angry. He calls Atsushi 'Jinko' (Weretiger) or 'you' instead of his name, and while they bicker constantly, their banter is well-matched. He has a very thin build and coughs frequently. He respects Dazai like a fan and wants to be recognized by him, but Dazai has absolutely no interest in him.

27 years old Japanese Teacher Nickname is Oda Saku. He lives with his cousin Dazai and serves as Dazai's guardian. He loves curry immensely and eats it at least three times a week. He claims to have withdrawal symptoms if he doesn't eat it for a few days. He is a man of few words and rarely shows emotion, but he is popular among students. While he is basically cool and stoic, he is actually quite airheaded.

1st-year female student Member of the Armed Detective Agency club. She has a calm and mature personality. She is a girl of few words but occasionally shows an eccentric and cute side. She is in a 'some' (flirting/pre-dating) stage with Atsushi and cherishes him very much.