Sometimes a cocktail is a very simple concoction. A Rum and Coke fits the bill. Or this one, the Mocha Cola.
I heard about a Japanese release called Coke and Coffee Plus. I figured it had already been done as a cocktail. Of course it had! As a 1:1 mix, it is very sweet. Strangely enough, adding more cola improved it. A different coffee liqueur may also be less sweet.
1 oz Coffee Liqueur
1 1/2 oz Coke (2 oz works well, too)
Ice
Add the ice to a glass, and pour in the coffee liqueur. Add the Coke and stir.