What exactly is "Five Fruits"?
"From context I infer that it's a sweet juice blend, maybe something like modern-day Hawaiian Punch; but I haven't been able to Google up anything about the name because everyone on the Internet wants to tell me about 1980s-era beverage Five Alive."
Due to the lack of historical data, it may be impossible to find out what exactly is "Five Fruits".
My own personal suspicion is that "Five Fruits" may be somrthing like the original Five Alive drink.
The original Citrus version: orange, lemon, grapefruit, tangerine, lime - Five Alive (Wikipedia)
Here’s a modern image of the drink
The “Five” represents the five fruit flavors in the drink. There has been a total of seven varieties, but the original was a blend of orange, lemon, grapefruit, tangerine, and lime. I have no idea what this combination tastes like; I’ve never had Five Alive. The memory I have of this product is entirely visual, etched into my psyche from a passing glance in a grocery store some 22 years ago.
While relatively popular in the U.K. today, Five Alive’s accessibility in the United States is limited. How it fell into reticence is anyone’s guess. - Juicy Details (Five Alive)
Five Alive Varieties
You can always use the modern Five Alive drink or Grenadine if you want. The one quarter cup in the recipe could be for either a syrup or a juice. A syrup would definitely make it more sweeter.