After the founding of the nation, demons were forbidden from cultivating into human form, and people were naturally forbidden from ascending to heaven at will.
The demon realm set up an office to register demons who had cultivated into human form. Heaven, of course, had its own way to prevent ascension: closing the Gate of Heaven.
But Heaven had been busy lately, and it was also time for the once-every-ten-years assessment of aspiring cultivators. So, on a whim, the Empress gave the key to the Gate of Heaven to the young princess, who was always lazing around, and told her to take charge of opening the gate. That way, when she inherited the throne as Heavenly Emperor the following year, she would have something on her resume to show the Heavenly Dao.
It was a good assignment, and the child was a good child.
But even gods can trip over nothing when their luck runs out. Watching the key to the Gate of Heaven fall into the clouds, the young princess let out a heart-wrenching scream.
And so, the young princess who sneaked down to the mortal world and the little dragon god who was forced to follow her arrived in modern society, preparing for the assessment of aspiring cultivators nine months later by searching for the key to the Gate of Heaven.
"Open up! Heavenly Court business!"
* A scatterbrained, adorably naive young princess x a grouchy little dragon who picks fights with everyone but bullies only those weaker than him
* Set in a fictional world. The mythology is partly made up and is not meant to stand up to scrutiny.
* A little story about looking for a key and catching ghosts along the way.
Theme: People must take responsibility for their actions.