This just so happens to be one of the eight possible endings you can end up getting from this game. For this, there seems to be only one point of interest that you will want to pay attention to, stated below:
*** Spoiler - click to reveal ***Point #1: Moocheriel, first visit
When you are heading to the focal point of the Moocheriel sphere, you will be given the choice to stop Saki from singing, or to let her continue. For this ending, we want her to continue singing. If you've given Saki the majority of the heart points, this point will differ in that we will lose Finnel and be fixed down this path. You will return to the Tower to head to Ku, deal with the new threat there, and be set with Saki's normal ending from that point on. "The Overlord and the Hero" is such a touching story, so be warned for the feels!