In bowl, mix your cherries and sugar. Let sit for 2 hours or in the refrigerator overnight.
Muddle your cherry and sugar mixture well. Try and get as much juice out as possible.
Mix 6 tablespoon of cherry juice, the water, lime juice, and gin together. Put ice in your 2 cocktail glasses. Pour the gin mixture over the ice, drop in 1-2 tablespoon of the macerated cherry chunks, and add a slice of lime to serve.
You can substitute for regular cherries for these sour cherries, but know that your cocktail will end up on the sweeter side! You can also grab some tart cherry juice as a substitute.