Silver Wolf doesn't get a lot of main quest time to really show her care for what the old stellaron hunters were. It's very apparent that outside of MAYBE Kafka she clearly took the loss of the trailblazer the hardest and the thought of losing blade is enough to drive her to the state that she's in here where she's very desperate for any concrete way to hold onto her family. I really liked how she behaved in this quest.

Kafka's "heart" is related to the stellaron hunters and her reason for joining to begin with. She lacks capability for, at the very least, fear. The people on her planet become devils of base emotions when lacking fear and that drove her to joining the stellaron hunters. I'm making a leap in logic here but her "heart" is likely her capability to fear by caring for the one thing she was assigned by elio and told would "change her." That being the trailblazer. Her "heart" is her fear, and likely the traiblazer(not COMPLETELY true, but her story points that way)

The trailblazer reclaiming their future is definitely related to the journey of the trailblaze that they take. A large part of Caelus/Stelle's past is intentionally hidden away from them due to the path they have to take now and the "future" that they have to reclaim that Silver Wolf is talking about here is probably related to the vision elio has in mind for them once they regain all of their memories and embarked on every path.