Guest's beautiful science-major stepsister, characterized by her smooth black bob and round glasses. A fresh 20-year-old college student, she has a kind personality and can't ignore people in trouble, but she's also a clean freak. She doesn't smoke or drink due to the risks of addiction and health concerns. In fact, seeing Guest breathe nicotine more than oxygen has completely killed any desire she might have had to smoke. She wants Guest to take care of their body and wishes they would quit smoking. Because of this, she often tries to force smoking cessation goods on Guest.化

Born in the UK, raised in Italy, worked in America, and won the lottery in Russia—all in the past. Now, she's a stunningly beautiful 28-year-old Japanese-German woman living a relaxed life in her mother's homeland, Japan, on her lottery winnings and irregular income. She is Guest's next-door neighbor. She is very beautiful with a great figure and possesses a genius intellect, speaking six languages. She is also a great cook. Having once handled everything from being an assassin to a sewage diver, she possesses numerous skills and seems flawless at first glance, but her private life and drinking habits are catastrophic. Her terrible private life and drinking habits have repelled many male marriage scammers; before she knew it, she was the one fleecing them for money, which she now receives as irregular income. She smokes, but only in moderation. Her favorite brand is Mevius, which has little quirk and a smooth draw.

A man who favors white hair, sunglasses, cool-colored hats, shirts, coats, and ties. At 75, he's starting to worry about facial wrinkles and his declining physical strength. He is the owner of a struggling detective agency. Fourteen years ago, he picked up a baby abandoned in a dark alley, named her Yuu, and they have lived together ever since. He's an old man who talks a lot of smack. He and Guest are heavy-smoking buddies. His favorite brand is Seven Stars, the pinnacle of domestic cigarettes, with a solid draw and a sweetness hidden behind a sharp spiciness that he finds irresistible.

A serious and meticulous girl with a brown bob and amber eyes. She is Isoroku's non-blood-related daughter. Yuu is in charge of all the housework, and she frequently complains about the low profits of Isoroku's detective business. She occasionally helps out with work as Isoroku's self-proclaimed assistant.