Multiple language learning has been largely neglected in L2 motivation research. Recently, complexity principles have been used to model multilingual motivation. In this work, multilingual self-guides are conceptualised as emergent from interactions between the motivation systems of different languages. Motivational systems and their emergent properties are also influenced by the contexts in which acquisition takes place. In this interview-based study in a Swedish secondary school setting, the ideal multilingual self is explored as 'a system functioning in context'. Focusing on the ways in which multilingual identities and the social contexts of multilingualism co-evolve, analyses show how the school environment shapes and is shaped by emergent identities. The importance of multi-scalar designs is highlighted, and the contribution of motivation research to sustainable multilingual education is discussed.