"The seedlings of romantic feelings, chemical reaction of love that occurs between men and women" is "케미"(kemi) in Korean.
It is abbreviation of "chemistry". Meaning that the chemical reaction, of love that occurs between the men and women. By two people were met, or occur development likely to subtle relationship in love, it refers to a like or attracted strongly change. 케미가 터진다 (Kemigateojinda / Kemi will explode), and it is used as 케미 커플 (Kemi couple). Also is not limited to the men and women of the couple, it is referred to in this way even in a couple of men with each other.