KAWUMM!

"Angels and Demons are invisible to the human eye"
Haniel and Balial are two Angels who need to exorcise a number of lowly Demons in order to advance in the pecking order. The problem is... they suck at it.
One day, Haniel is tricked into thinking he's somehow been demoted to a mortal when an old, seemingly human woman asks for his help grocery shopping.
He puts the blame on his partner's lacklustre performance, and follows the elderly woman. Unbeknownst to him, they're being misled into a Demon ambush. Strangely enough, their higher-ups are there to rescue them. Suddenly, Balial transforms and Haniel loses conciousness.
Thinking his only friend is gone forever, Haniel must continue facing Demons,
while he's being tormented by extreme self-loathing for how he used to treat him.