After a new energy source is used to power an entire city, a young cleaning lady is called to protect the city from supernatural threats called Jinn that are attracted to the energy source. The Jinn take over human bodies and give their hosts supernatural powers.

This new energy source of yours has something to do with the Jinns? What I mean is: is there a secret behind this new source of energy? It would be interesting if there was a relation between the energy source and the supernatural. Is it a quantum/ nuclear thing, the god particle or something like that? Or is it an old stolen relic that powers the city and that belonged to the Jinns a long time ago?
The cleaning lady part is cool and comic, I like this protagonist but I also need a bit more information. Why is she special? the ?cleaning? is a metaphor for a killer or is she really a cleaning lady? The cleaning ability will be pertinent to the story?
The part about the Jinn taking over the human bodies is very cool? it reminded me of The Body Snatchers and Battlestar Galactica (less): not knowing who is the enemy raises the tension (they are hiding in plain sight).
The supernatural powers transferred to the host are nice but the powers are not really given to the host because their body (and mind?) has been taken over? I think there should be a problem when a Jinn invades a weak human body: there are the cool powers but the body can't handle the supernatural power for a long time or something? like the character Doro, in the Wild Seed book (Octavia Butler).

When a new power source allows djinn to take over the body of defenceless humans, a meek cleaning lady the last descendant of supernatural warriors must fight to save her city.

>>>An otherworldly being imbues an unassuming young cleaning lady with powers to protect a city from supernatural threats attracted to the new energy source used to power the city by a power hungry inventor.

Why doesn't the otherworldly being do the job herself?? Why does she subcontract the work to the cleaning lady?

Kind of smacks of an improbable?deus ex machina gimmick, only in this instance a deus ex machina to kick start the story rather than resolve it.

Of course, you are allowed creative license in inventing your imaginary world, but within that world actions must be internally consistent and logically motivated according to the rules you have set up.? In this imaginary world, what is the logical reason an otherworldly being doesn't intervene herself?? Why must she get the job done through a proxy?