Warring States Picture Scroll
Warring States Picture Scroll (Sengoku Emaki) is a section in the game where you can see the special event pictures which appear in the game. There are a total of 30 different pictures which you can collect by doing certain things in the game. It is impossible to get all 30 event pictures by playing the game once because some of the pictures only appear when you use a certain character.
As you can see, I have all the event pictures except for the last one. I have a theory on how to get this picture, but I don't have the time to test the theory out. But if you want to have a shot, then try making everyone 'happy'.
The epilogue picture that you get at the end of the game (after the credits) depends on the character's 'koukan' (happiness) points. For more information about koukan points, see the Walkthrough.
So I'm guessing that picture 30 is a group epilogue picture. So if you can get a high amount of 'koukan' points for all the characters, then that might result in Sengoku Emaki 30.