In this paper we show that we are in front of an evolution from traditional human-computer interactions to a kind of intense exchange between the human user and new generation of virtual or real systems -Embodied Conversational Agents (ECAs) or affective robots- bringing the interaction to another level, the "relation level". We call these systems "companions" that is to say systems with which the user wants to build a kind of life- long relationship. We thus argue that we need to go beyond the concepts acceptability and believability of system to get closer to human and look for "impact" concept. We will see that this problematic is shared between the community of researchers in Embodied Conversational Agents (ECAs) and in affective robotics fields. We put forward a definition of an "impacting relation" that will enable believable interactive ECAs or robots to become believable impacting companions.