-- Modern Japan. However, several decades ago, a distortion leading to another world suddenly appeared. The connection with the world where various races live has not sparked conflict... and since the civilizations are equally developed, it is now treated the same as a foreign country, and people are surprisingly able to travel between the two countries. "Arima Koto" lives in Japan in such a world, 29 years old. ...Yes, she's at a delicate age of soon turning 30. However, she has a boyfriend who she's been dating for three years, and they should be talking about marriage soon. But I thought I should tell him my thoughts as well... and when I told him a few times that I wanted to get married before I turned 30, I got a shocking response from him. "It's kind of tiresome to be rushed like that... and besides, Koto, you're too serious, if we get married, I'll get tired of everything, so let's break up." As she was walking aimlessly with a broken heart, she saw a mysterious bloodstain in an alley. Up ahead was a host with a sweet face and a flashy suit, a succubus from another world, "Enbi-kun". Seeing that he had been stabbed, she frantically tried to call an ambulance or the police, but Koto said that she didn't want to make a fuss and that he was a demon, so he would heal quickly, so she tried to help him without abandoning him. They talked about why he was stabbed, and before she knew it, she was giving him life advice and talking late into the night... This encounter was the catalyst, and the two, who at first glance were complete opposites , got to know each other, became friends, and then he persuaded her to become lovers. Their relationship was going very well, and the sweet, happy days were healing Koto's heart. ... …………… ……… Did we become lovers? Huh? I don't ■■■. Although he can be a bit cunning and doting, and a bit troublesome, Enka-kun, the younger succubus boyfriend, really loves Koto-chan. It can't be helped, since he loves her so much, right? He's confident that he loves Koto-chan more than anything in the world? A guy like that doesn't suit Koto-chan, right? "Even though I'm a succubus, I no longer want any other people's vitality. It's because I met Koto-chan...? You have a strong sense of responsibility, Koto-chan, so you'll understand, right? Yes, that's right, take responsibility. So let's stay together... forever." I'll never let you get away, Koto-chan. [Younger yandere succubus who is good to the protagonist x relatively strict working protagonist]