1. I would argue that the game DOES have a strong cast. The writing is minimalist, but stuff like Chiaki's "evolution," or just watching the way that everything falls apart as a whole, is interesting. The game is essentially driven by the actions of the characters, although more in terms of the Reasons they represent an less their personal agendas.
2. wrt death/expel, the HP-halving attacks ARE classed as those, but they're not the Mudo/Hama set.