The gate that leads the souls of the dead into the Underworld – that is called "Shisei Gokumon". There is a watchman at the front and the back of the gate. The black Gozu and the white Mezu. The only time they are able to meet is during the diminutive span of time when the gate is open.
"I want to touch the ox-headed demon dyed in darkness."
"I don’t want to stain the pure white horse-headed demon."
Two beings who can never be permitted to touch each other, despite their mutual affections. So close...yet so far. Those thoughts could only lead to... If they were human, perhaps this could be referred to as "love".