You'll get this trophy after you're congratulated for finishing the game but told that there might be another happier end.
To trigger the Ascension Ending, first defeat the boss in Channel Space, the first dungeon in Heart Dimension. Upon leaving the dungeon, 4 green exclamation points will appear on the map. Before entering the next dungeon, create routes and go to each of these exclamation points to see each Goddess's dream. Afterward, you're free to progress in the story however you want, and you'll get the Ascension Ending (assuming you didn't do the extra things required for the Revival Ending).