Oretači no iru sekai (E34)

Saya has returned and her year long absence wasn't wasted. She easily kills 2 Chiropterans, but collapses shortly after. Kai and Lewis take her back to Gray's to rest up. After being around her for a short period, Kai realizes this is not the Saya he once knew. What happened to Saya over her year long absence? (Prime Video)