Make Shiori say Suki Desu:
After Shiori's description of the legend when you see her standing under the tree before the opening movie, enter the standard Konami cheat code on the 2P controller to make her say it.
up, up, down, down, left, right, left, right, X, O on 2P controller
Shiori will say Suki desu (I love [you])
up on 2P controller when mouse is in 1P port
Shiori will say Suki desu (I love [you])