you need to find Broken IC Chips from monsters. Bring those to 'Virtual Girl' in the VB
Room in Home III she will change it to Comp Hack A or something like that.. then you go to the NPC with the problem.. link up .. and go into their Comp to kill the monsters/viruses lurking within. After you defeat the boss, you either get a key or something from the treasure boxes and give it to the NPC when you get outside. They will give you a Demon as a reward some include [Kikuri-Hime], [Shiishaa], and [Succubus]. There are others depending on the NPC the rewards vary.