I had this thought quite some time ago (soon after I discovered Tenchi Muyo) but it recently recurred to me.
A young man is constantly followed by a demon. In my mind's eye, the boy looks like the kid from Fooly Cooly (originally he looked like Tenchi) and the demon looks like Ryoko. The kid is walking down the street when the demon pops halfway out of a stop sign (like Ryoko's phase through walls ability, except only half the demon is there) and laments about the young man's cold heart and how he is killing her by spurning her shows of affection. He continues to walk down the street and she appears halfway out of various signs, the sidewalk, parked cars, etc until he finally gets so fed up that he hushedly but angrily barks, "Begone, demon!" (he would shout from the top of his lungs but for the attention it would bring; other people are oblivious to the demon's existence but not his). At these words, the demon would burst into tears and disappear back through whatever portal currently bisects her.
Throughout these meetings, the boy comes off as a cold-hearted, uncaring jerk while the demon comes off much like Ryoko when she says "I guess nobody can love a demon". In other words, she seems sincere and sympathetic to the audience in both her love for the young man and her torment at being a demon in love.
I do not know what catalyst brings about the end to the story but it happens as follows: the young man finally acquiesces to her entreaties and just as he touches her, her eyes glow red, a wicked smile plays across her face, her features twist from an attractive young woman to a demonic countenance, and with a flash of movement, she grips the young man by the very soul (utilizing the "transparent look-alike" cartoon ghost effect). A gaping hole of flames and smoke opens at their feet and she plunges into the depths with her treasure in tow. The boy's body falls lifeless to the ground as the chasm seals behind them, leaving only the echo of his tortured screams.