The Tachikoma that Batou uses most and also gives natural oil to, awakens at night and heads into the city wanting to learn.  It helps out a little girl who's looking for her dog and along the way finds a cyber brain.  After it returns Motoko demands that no more natural oils be given to the Tachikomas and that the brain be scanned to determine what it is.  When a Section 9 investigator get lost in the brain with no barrier, Motoko must dive in and see what's going on.