Hi, thank you so much for playing and reviewing. Calling her Vivienne didn't actually trigger second story, you could've called her anything and she would've ignored you and called herself Vivienne. The new stuff opens up after you saw the hidden end and start a new game. If you want to see the endings you missed, if you played through the second story and reached the last ending, or if you just open a save file from before finding the hidden ending, you can get back to the first story and pick the two options you haven't picked yet. (Look at senpai and watch tv)