Volume four continues with more of the same antics with Hitoshi Kobe, Saati and Toni. But this time there is a new wrinkle: the introduction and "live" appearance of a new sibling for Saati and Toni - Forty!! Forty's programming was scrambled during a fight between Saati and Toni, so Forty has characteristics that both wanted in a sibling. Only manifested as a split personality. Forty has a male persona AND a female persona. Both show up to cause new mayhem.
Saati deals also with an identical a.i. imposter, and gets to show her maternal side.
This book continues in the same vein as the others. I didn't enjoy it as much, but that's probably because I didn't warm to the new Forty character and he/she is prominently featured in the storyline now.