Yeah, kinda figured this was how it was going to turn out.
The way out is to literally unite together, failure to do so means that there are no resolution.
It's one where clear even heads would be able to logic this out where clearly they all should use their powers combined. Sure, they return to square one on their issues but they have gained additional support outside of themselves since they all have circumstances that all requires additional assistance, but they were trying to resolve those singularly by themselves to begin with.
While it wouldn't resolve the issues they had, they would still get out of the immediate issue of them being trapped and at risk of death, while also ensuring that nothing would come back to create additional friction afterwards.
Plus, creating this rising tension while everyone has access to a superpower means that hot headed action would immediately lead to complete mutual destruction.
And yeah, kinda figured they were hiding something about Takakura's death too. Too much of a Chekov's Gun not to have that pulled up. And ultimately that hidden shared criminal guilt is what pushed them to abandon reason. After all, even in their shared crime which lacked any and all reason, would leave them in a situation where they would still end up backstabbing one another as only one person could end up becoming her lover.
In this case, though more bittersweet, there is at least one instance of actual Justice. It was vigilante justice, it was vengeful retribution, but it was a form of Justice and brought to light a crime that otherwise would've remained unknown to her. Kinda wish she would've had at least a more happy ending, staying alive and moving on. But I guess her deep love for her dead boyfriend paired with the sense of betrayal and the weight of taking their lives all kinda sank way too far to recover from.
Basically:
Very predictable, but still a generally good baseline story. When is the second season of Sunranger?