I warned you about stairs bro, i told you dog!
Contrary to Sakubo's claim of being siblings, both Saku and Bo are controlled by an eleven year-old boy named Iori Nakanishi (中西伊織
. Saku appears to be a 'big sister' personality created by Iori in order to protect him against other people, hinting that Sakubo's player may have Multiple Personalities or Dissociative Identity Disorder. Iori originally had an older sister named Sakura (桜, but she was stillborn.Depending on the players actions, the Saku personality can either remain or go away for good. Returner OVA suggests the canon action is to allow "Saku" to stay.