Akiha will be back from her canon update for the Warrior Princess' call. As she's not actually close to any of the captives, she'll need to be convinced to participate.

As much as she has the skills to be a good ambassador, she's not the negotiate with terrorists type. Once she IS convinced to help, she'll be able to restrain the skeletal serpent with her demon ability long enough for someone to destroy it. She's also one of the best defenses against anything flaming/lightning when it comes to protecting the flying machines.

But again, she needs convincing.