[Context & Motivation] The connected vehicle can be seen as a system within a system of systems (SoS). Functions that can be experienced by the vehicle user are often provided by the interaction of several systems that are managed and operated independently. [Problem] Due to the managerial, operational and evolutionary independence of constituent systems (CSs) in a SoS, requirements can evolve and constantly change over time. Therefor, linear and top-down requirements engineering methods can not be applied without significant adaptations. To define requirements for the development of CSs in a SoS context, new tools are needed that support the continuous and iterative specification and alignment of requirements across different levels of abstraction. [Principal Ideas] We propose to integrate the behavior-driven development (BDD) approach with an intuitive and scenario-based modeling of functional requirements. In this way, stakeholder expectations can be structured via features and documented in natural language as usage scenarios. Based on the usage scenarios, the modeling of functional requirements can be driven by tests. This combination of BDD and scenario-based requirements modeling allows the automated testing and analysis of requirements to support the iterative specification of requirements and the alignment of stakeholder needs. [Contribution] In this paper we show the tool BeSoS that supports the iterative and behavior-driven specification of requirements in a SoS context. We propose a method and describe the architecture and inner workings of the tool. A demonstration of the tool is available here: tbd