Emperor has a tendency to split. I think that is what causes the rotten fruits you are seeing. If you want less acid, let them get purplish red before picking. If I remember correctly, Chakrapad (Emperor) is not grown much in Australia because it is suposedly too sour. Here in Florida, they are not sour. Since it was bred in Thalinad, I assume that it has to do with the amount of heat we get durring ripening. Maybe you are more like Australia in Hawaii? Also, after looking more closely at the pictures, I have a few thoughts. It appears that the stem in the fruit comes straight down in your picture. In Emperor the stem typically attaches to the top of the fruit at an angle. Also, Emperor has a reddish flush when putting out new leaves. If your flush is bronze, it is not Emperor.
This is very insightful and helpful. Stem comes straight down and no, we don’t get the heat of Florida or Thailand. Highs at this location have been topping at about 80 and this summer has been cooler than normal. I will have to check for flush color.
Interesting characteristic, red flush, as I understand Emperor was developed in Thailand from Hainan King lychee. My Erdon Lee seedlings are related and also flush red, quite beautiful!