1. Play through the entire game once going for either Finnel or Saki, meaning all 3 hearts go to them. fail to defeat Myu, stop Saki's song for BAD ENDING
2. Reload to before you stop Saki's song to let it NOT stop, and end up with NORMAL ENDING for either Finnel or Saki, depending on the choice of your pure playthrough.
3. Reload to before you fight Myu, win the battle, stop Saki's song, get TRUE ENDING for Finnel or Saki, depending on your choice.
4. Start a New game+, so that you migrate your levels, money and DP, making a subsequent playthrough much easier. Now go for a pure Saki or Finnel route ( the one you DIDN'T choose ) and make sure you have a safety save before the battle with Myu and the last choice.
5. beat Myu, make safety save at Saki's song choice, don't stop the song, get NORMAL ENDING for the second reyvateil.
6. Reload to before the Saki's song choice, stop the song, finish the route, get TRUE ENDING for the second reyvateil.
7. Reload to Myu battle safety save. choose the other reyvateil so you have a 2:1 heart ratio. Beat Myu, stop Saki's song, and the MOST final part of the game you can make the decision for the ending is JUST before you have Sasha help you put up the Satellite and have Cocona sing the song to power the tower. So make a safety save just before that, from here complete Tylia's cosmosphere, choose Tylia over the world in the cutscene that follows after the event for TYLIA NORMAL ENDING
8. Reload to safety save, complete Tylia's cosmosphere, in the event that follows choose The world over Tylia. get TYLIA TRUE ENDING
9. Reload to safety save, don't complete Tylia's or anyone else's cosmosphere, go through the event and you'll end up with COCONA ENDING