The biblical god finds the world's faith in him lacking due to the widespread hedonism but can't just smite people because of a bet he has with the devil so he decides to make use of a loophole that leads him to garner more faith for himself by incarnating as a human girl with the goal of rising up from the bottom and becoming the idol of idols sans the use of any miracles in public eye else the devil will smug it over his head.

I call this one "Smite Me, Almighty Idol!".

- MC is god's young upstart producer who traded his soul for success and takes on the job because it's a ticket to heaven if the scheme works.
- God poses as MC's long lost younger sister who wants to break into the idol biz, Kamino Shouko. 
- The bet involves getting more than a certain percent of the world's faith by a certain date and Japan just happens to have the right numbers to get it done and it came about because the devil taunted him into it. 
- Rules state god can't send any more prophets or miracles to get believers but allows him to get faith under another identity since those believers still fall under him.
- The devil is just a smug classy ass in a suit having fun. No real downside for him to lose, he just enjoys messing with the big guy.
- God is allowed to twist reality into proving the existence of his avatar and facilitate the idol career though no public acts.
- God is beyond common sense and has trouble adjusting his viewpoint down to human level so it results in a very obtuse, insensitive and prideful little girl who has no trouble abusing power when it's allowed.
- God keeps Gabriel around as a level headed little girl too. Gabriel's adapts to human society well and helps keep god out of trouble, particularly at the school they have to attend to keep up the cover. MC is very concerned that gab is told to keep the horn that ends the world handy at all times.
- God is initially a solo act but doesn't gain much traction because of the many faux pas that happen so he gets partnered up with an angelic human girl as a duo that takes off.
- The girl can't ever know that god is her partner and she unintentionally tempts the MC into committing scandals and crimes. The devil happens to be her foster parent and gives her advice loaded with hijinx.