1 + 1 = . . . 3?

Kim Junmyeon is tired. He's lived for thousands of years already, and he's sick of life. He's visited tons of places, seen billions people and all of this is dull for him. Colorless, boring, and lifeless. He had everything, but nothing lasts forever. When one day, he meets a young girl with a cold, expressionless face, he became interested for the first time in so long. And... it