Fear
"I could help if you're willing." Cassandra says not unkindly, but Sera bristles at the suggestion and jokes instead (always deflecting); there's something about the pity in Cassandra's eyes that makes her feel uncomfortable.
Faith
For what it's worth Sera had little of it, and Cassandra was losing hers, losing everything.
Burning
Cassandra lead the charge, a beacon of hope in a desperate time. Haven was burning and they were helpless, but she was all they had.
Unbreakable
The Seeker's stoicism was a clever front, Sera knew, though the walls she built were impenetrable, a challenge.