The first art is just a crypt with bones in it, the second a grave marker. The traitor is Saint Sebas, since that is his tomb. Why he would be considered a traitor is still a mystery, although clearly not everbody thinks of him that way.
The dialogue is meant to hint that the Rabbit is associated with the tower, although I kinda screwed up putting him on the bridge totally out of place after he leaves the letter. That positioning is meaningless.
The body in the house is not the daughter, but maybe what she brings to the merchant.
Dark aspect does more damage the more armor the target has, but only Lizardmen and glowing enemies have armor, so it's not particularly useful to the player.
In the sequel, armor is more like a barrier that can be removed with attacks, so dark damage instead gets bonus armor burn with training.