Well, you would be playing the special one, the main character who has an important role in shaping the future. This future has three possibilities which are the good, bad or the hard neutral route. The important person can't shape the future themselves and so they can side with one of the goddesses to help them get the future they desire. You can have both but it is no easy task. I would be playing both the goddesses who will try and sway you from the path you picked. The chosen can go from good to bad to bad to good if you wish as humans have a change of heart quite often or one's ideals change. 

On top of that, the bond you have with the goddesses give the special one powers over time, knowledge on how to handle weapons or magic based on the goddess picked. Both of the goddesses give you some passive and active powers such as the goddess of light will give you the ability to rain golden arrows from the heavens and heal others or yourself. The goddess of darkness will allow the special to bring forth blades of darkness from the ground or any surface as well as grant the passive power of creating any toxin/poison in existence. 

This, in turn, will influence the way they handle things, a good deed or bad deed will affect the city they hail from. This, in turn, affects the way the they fight the titans who are coming. Unknown gods and goddesses are long forgotten by most.  

In short you build the city into what they want and then they have to defend and defeat the incoming dangers of the titans and its legion. It is like a slice of life/fantasy/modern/drama and such.

I hope this clears it up, if not I will have to try and simplify it better.

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