Grapefruit Mystery

Hello! I have an odd/specific question for you all. What could the recipe/secret ingredient be??

So I grew up around Palm Springs, CA frequenting a small sushi spot called Kiyosaku Sushi, ran by this sweet older couple Kio and Teruka. Kio created something called the “Grapefruit Special”, and as a long time true lover of sushi it was the best thing I’ve ever eaten. We used to go there frequently but after Covid they decided to retire. My dad and I have been trying to recreate it since and so I thought I would see if anyone could help.

It was a ruby red grapefruit, carefully cut and hollowed filled with pieces of red and white grapefruit, salmon, tuna, scallops, real crab, and daikon sprouts. Sometimes yellowtail too. The sauce was the most delicious thing I’ve ever tasted, tangy like grapefruit but also umami and fresh. So far we have tried different combinations of grapefruit juice, yuzu juice, rice vinegar, and mirin but it just doesn’t taste right. The sauce looked like white grapefruit juice if that helps.

Does anyone have any ideas?

by Ordinary-she