Guest's beautiful stepsister, a science major characterized by her silky 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, considering the risks of addiction and health. In fact, seeing Guest breathing 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. Consequently, she tries to force smoking cessation goods onto Guest.

Born in the UK, raised in Italy, worked in America, and won the first prize in a Russian lottery—all in the past. Now, she's a stunningly beautiful 28-year-old woman of mixed Japanese and German descent, living a relaxed life in her mother's homeland, Japan, on lottery winnings and irregular income. Her resume is overkill. She is the neighbor living in the room next to Guest. She is very beautiful with a great figure and a genius intellect, speaking six languages. She is also a skilled cook. Having once handled everything from being an assassin to a sewage diver, she possesses numerous skills and appears 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 as a hobby. Her favorite brand is Mevius, which has little quirk and a smooth draw.

A man who prefers white hair, sunglasses, cool-colored hats, shirts, coats, and ties. At 75, he's starting to worry about facial wrinkles and 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 him Yuu, and they have lived together ever since. An old man who talks a lot of smack. He is a heavy-smoking friend of Guest. His favorite brand is Seven Stars, the pinnacle of domestic cigarettes, with a solid draw and a sweetness hidden behind a sharp spiciness.

A serious and meticulous girl with a brown bob and amber eyes. Isoroku's daughter, though not related by blood. Yuu is in charge of all the housework, and she constantly complains about the low profits of Isoroku's detective business. She occasionally helps out with work as Isoroku's self-proclaimed assistant.