Combine 1/2 cup rice vinegar (not seasoned) and 1/4 cup each sugar and water in a small saucepan. Cook over medium-high heat until the sugar dissolves, about 2 minutes; let cool. Combine 1 cup each shredded daikon radishes and carrots in a bowl. Add the vinegar mixture and refrigerate 30 minutes. Stir in 1 thinly sliced jalapeno and 1/2 cup cilantro.