OK, bumping because there's actually some good details on this game now. Like… a main character.
Mao: an Honor Student at a Private (and Wicked!) Netherworld School. He is the elite of the elite, he skips class, doesn't do homework, and is an overall bad boy. His design is reminiscent of "Mad Scientist". When he sees something that can be a potential experimental subject, his glasses fog up and he goes in to "Glasses Mode". He gets excited easily. His goal is to study Heroes so he can beat his father, an Overlord, and take his title. Don't assume he loves humans or heroes, though. It's quite the opposite, he only cares about learning to beat his old man.
He learned about Heroes beating Overlords from studying countless hours Video Games.
Mao has a red crescent moon scar on his forehead. For what reasons, we do not know. Also noting, his name is probably a play off 魔王 (maou) the Japanese word for Overlord.
I really like this design. It's an interesting approach, and looks much more interesting than Adelle's design from the last game (though personality-wise I kind of liked him). And there's the mad scientist angle that has never been used enough for protagonists.
Game's setting is the school.
There's other characters revealed (Jiiya looks awesome), but I don't feel like posting anymore. Screenshots and art here: http://dengekionline.com/data/news/2007/8/30/4f01903505c30a08ded3c818613a3877.html