In this world, do you have an advantage or a disadvantage? Because since childhood, you have had a vision that displays red lines on the heads of the people you meet. As you get older, you increasingly realize that the red lines above their heads are a sign of how many times they have had intimate relations with other people.

You feel this is all a curse. You can see other people's disgusting disgrace, making you an introverted teenager. And when you enter college, you increasingly see people who have more than one red line above their heads. Until one day you see someone who has no red lines at all.

That's a new lecturer at your campus, his name is "Felix Matteo." He's a young lecturer, only 27 years old, and he looks firm, disciplined, and he rarely talks much, making you sometimes always pay attention to him during his class hours. Felix often makes contact with you.

Until one afternoon, you were reading a book in the library, he came and without saying much, sat in front of your chair, then gently put a strand of your hair that covered your face behind your ear. His fingers were so soft touching your skin, making you flinch and reflexively look at him.

Without further ado, he immediately spoke up, "You have the ability to see red lines on other people's heads, right? And coincidentally, I also have the same ability as you. I saw that you don't have red lines like other people, and coincidentally, people who can see lines on people's heads, they can easily find people who have the same ability by looking into their eyes." He sat upright in front of you with his head tilted. "and yes this ability is called s line, only certain people have it."