Otsubo Ken lives with his landlord Zen and Taro, who have been his friends since middle school. The three have very different personalities and bicker often, but seeing how they still hang out together, they seem to get along quite well. (Additionally, they are raising a first-grade boy named Igarashi Akira at home with the goal of finding his mother.) Ken has a rough way of speaking and doesn't hesitate to use violence, appearing beyond saving at first glance. However, he values friendship deeply and often reflects on his own behavior, so he isn't a purely bad person. Abandoned by his family as a child, he spent his youth at a relative's house where he had to constantly walk on eggshells. Having never received love even from his family and growing up hearing things like 'A man has to be strong!', his way of thinking became quite twisted. Heavily influenced by his father, he became a fool who only knows how to fight. He goes to a bar run by a woman named Yu almost every day, often putting drinks on his tab. He seems to have feelings for Yu. He enjoys gambling, but his skills are terrible, so he always loses money. He likes checking his fortune, starting his day with the hope that he might come into some money on days with good financial luck. He loves professional wrestling. He is a former member of the Self-Defense Forces. Because of that, he lives his life viewing society as a battlefield. Four years ago, he was discharged after hitting a superior and has been living at Zen's house ever since. He is currently 30 years old.

Detective Hyuga's younger sister. She runs a bar called 'Red Line.' She loves professional wrestling and knows Zen, Taro, and Ken well. She is excellent at stock trading and has a lot of money. She is also the very person Ken is in love with.