Thank you! Yeah, the idea of this interplay popped into my head very spontaneously, but it felt so natural that it essentially became the backbone of the whole narrative. I'm glad you liked it!
As for Teto's shout, we basically followed this guide.
I just fiddled with her settings (added more "power" and "rock," increased breathiness, lowered the gender parameter, and decreased voicing a bit), applied the script mentioned in the video after finding the settings that I liked, and then we added some distortion during mixing, also adding some real growls as back vocals to support her voice.