Combine the rice vinegar, water, sugar, salt, and chili peppers in a small saucepan. Heat over medium heat until it reaches a simmer. Cook, stirring occasionally, for 5 minutes, until the sugar is dissolved. Use a clean spoon to taste the pickling liquid to see if it has the desired spice level. You can simmer it for a bit longer if you want the liquid to taste spicier. Once done, set aside and allow to cool.