Cruz takes a few minutes to explain that Saten's true Fragment ability is heat absorption, where he can absorb the heat in the air around him and from some Needless attacks and then unleash it upon his enemies with his Fourth Wave attack. With this in mind, Adam Blade and Eve continue fighting him.
Meanwhile, Teruyama, Seto and Solva are fighting the mysterious girl, who somehow melts Seto's sword in half. Teruyama manages to punch the girl's mask so hard it breaks, revealing her true identity. For the two of you who weren't paying attention, it turns out that the mysterious masked girl is actually Cruz's sister, Aruka.
In a long-winded dialogue, she reveals that she was a member of Simeon's Elite Four who joined the Resistance in order to spy on them. She was the one who lured the Resistance into a trap that would wipe them out (see Ep #1), and then she faked her own death, hoping that the Testament in the sewers would kill Cruz for her.
All of this was to get some kind of hidden data chip the leader of the resistance held. Apparently, he secretly placed it in Cruz's locket, as her brother was the one person Aruka wouldn't kill outright, but now she decides to kill Cruz and take the locket anyway. With her powers, she's able to use Seto and Solva's attacks against them, and then delivers a direct burst of microwave radiation into Teruyama's chest. Just as she's about to kill Cruz directly, Adam Blade grabs her wrist.
No, they are still not out of the Third Shelter yet.