I think the teaser showed a little more than just a dark theme and a luminous shape.
Judging by the red eyes in the darkness and the graffiti at the bus stop - "god" being crossed out while the word "hell" isn't, I would guess that this will be a game set in a (post) apocalyptic setup.
I'm guessing that "Light" will play a big role here, probably as a deterrent to the demonic forces that lurk in the dark.
I assume that the "Lighthouse" will act as our protagonist's and his harem's base of operations where they are safe and think about / prepare how to save themselves or the world even. A lighthouses function is, after all, to shine a beam of light into all directions (deterring demons, who are weak to it), while at the same time being a beacon that humans and non-demons will flock to. The luminous shape is probably the key to it, similar to what the bright lord's function is in this current game. That shape will either possess our character our guide him.
I think there will be (lots of) loose parallels to Bright Lord.