[@Ceta de Cloyes]

As far as the inspiration I got from Gargantia, it was the ships they are living on, and how they collect rain. Things like that. The mecha robot things are a no go for this RP. 

I've never play SOMA, base on the google images, it looks like an underwater settlement horror? As for settlements underwater for this RP, that could totally be a thing, but I am kind of hesitant because there is already a lot going on as far as places. 

I don't really know what you mean by rapture reference. The great flood and natural/man made disasters that covered the earth would have been considered biblical or "gods wrath" by those who were religious at the time.  

AI more then Siri or an Amazon Alexa was not established before the end. They could have been created on the Mars colony, but it was not shared on earth. So the people that crash landed form Mars would have knowledge of it, but they wouldn't actually have the tech. 

There [i]are[/i] new creatures of the deep, scary sea creatures, new fishes, and gigantic animals that once were small, like turtles or something. 

As for NPC, they are basically Characters that are around that no one is officially claimed or are playing as their own, so we as players can use them as we wish in our IC writing. For instance I would write as Iris walking around the Docks, and can converse with an NPC who is selling wares or something. Adoptable means that if someone wants to take the NPC and make an official CS for them, then they are claiming that NPC as an official Character of their own to play. It is basically someone taking them on as a main character.