Once you've completed the main game, a new option opens up: Bobo Video. Bobo offers you some new Ero scenes if you bring him three of a girl-type monster. There are eight all together: Scorpion, Sleepy, Priestess, Nun, Koyuki (Ice girl), Panda, Black witch, Sorceress, ???, and Angel. You can see their images by clicking on the new tab in the Home screen.
So how do you capture them? Well, only Matis can capture them. To capture, Matis has to deliver the killing blow. When this happens, you'll receive a message telling you about the capture. When you return to home, you'll have a short conversation with Bobo and deliver your captive(s) to him. When you've captured one girl three times, an ero scene will open up in the Bobo Video area.