In this paper we explore the opportunities, challenges and best practices around designing technologies for those affected by self-harm. Our work contributes to a growing HCI literature on mental health and wellbeing, as well as understandings of how to imbue appropriate value-sensitivity within the digital design process in these contexts. The first phase of our study was centred upon a hackathon during which teams of designers were asked to conceptualise and prototype digital products or services for those affected by self-harm. We discuss how value-sensitive actions and activities, including engagements with those with lived experiences of self-harm, were used to scaffold the conventional hackathon format in such a challenging context. Our approach was then extended through a series of critical engagements with clinicians and charity workers who provided appraisal of the prototypes and designs. Through analysis of these engagements we expose a number of design challenges for future HCI work that considers self-harm; moreover we offer insight into the role of stakeholder critiques in extending and rethinking hackathons as a design method in sensitive contexts.