Melt chocolate in top of a double boiler over simmering water, about 5 minutes. Remove from heat and let cool.
Beat aquafaba in a stand mixer on high speed until firm peaks form, 10 to 15 minutes. Add sugar gradually into the mixture while continuing to beat. Fold in cooled chocolate gently.
Spoon mousse into small glass cups and chill in the refrigerator for at least 4 hours before serving.