Place the water in a small pot on medium-high heat, and heat to a boil.
Add in the sugar, coffee and agar, and whisk vigorously for a few minutes until everything is completely dissolved.
Remove from the heat
Pour into an 8"x8" pan, and allow to sit on the counter to cool for about 30 minutes, then remove to the fridge to set completely, about a couple of hours.
Cut the jelly in strips first one way, then the other. You can make the cubes as small or as large as you like using this method.
Scrape up the cubes from the pan and place in a pretty dish or glass to serve.