Well I got the Bad Ending only when I got all Sun points but none of Moon's points. For the Good Ending I have a theory. I think Sun has a lot more points than Moon. So maybe we need to have the same amount of points for Sun and Moon?
Another thing se could try is looking for the CG's? When you have the right choices with Moon you get an extra CG and one where his face changes. I've only got Sun's changing CG (Not an animation) So maybe we should look for his extra CG?