The limitations of fixed traditional public transportation justify the exploration of demand-responsive mobility, particularly in low-demand rural areas. Departing from the Guimabus transportation system, which operates in Guimarães, Portugal, this research proposes a demand-responsive service that complements its peripheral areas with the aim of reducing private vehicle dependence, achieving more sustainable overall transportation. A case study is developed assessing the population served by Guimabus and its frequency in different parts of the geography. Then, a demand-responsive system is proposed, servicing rural areas of the outskirts of Guimarães. Different demand-responsive problem configurations are set up and solved using our own computational scheduling algorithm. Our results narrow down the minimum level of demand necessary for the demand-responsive to perform efficiently. Furthermore, they show the relationship between the balance of fleet resources and demand. Adequate usage of the fleet emerges as a necessary condition to improve, in terms of sustainability, with respect to private transport.