Fridge Brilliance: Even though the pre-StrikerS characters don't appear here, the Sound Stage X give you the feeling that the Forwards are not dependent from them and they can solve their cases alone. Especially Teana should be able to solve a case as an Enforcer without the help of an another (with the exception of their aides), as all Enforcers are supposed to be top investigators and superb mages - Chrono and Fate were the only Enforcers in their respective cases. It's also demonstrated how busy the characters actually are and they cannot meet each other everytime. Nanoha and the others trained the Forwards to do their duties by their own, without the help of their former superiors, unless it's an special emergency. This sound stage shows how much they Forwards have grown.
Nanoha and Hayate wouldn't fit in this case. Nanoha could only destroy the Mariages and save people, but Subaru is a member of the Rescue Force and that's her job. Subaru, Erio and the others are strong enough to destroy the Mariages by their own. Hayate fits only for high commands, and her magic abilites are rather impractical, even though, she could freeze the inferno. And investigation is Teana's speciality, Fate has probably her own case, and she couldn't help Teana in her case, as Teana is supposed to do it by her own.
Jerkass Woobie: Runessa has done some terrible things, but once you hear about her past, you can see why she has grown disillusioned with the world.
Moral Event Horizon: The mastermind behind the attacks, Runessa Magnus, has crossed it with the resulting body count from the plan, arguably putting her beyond the point where it is possible to earn redemption like most former antagonists.