Design for mood regulation is an emerging design area that is gaining growing interest. However, there is limited guidance on what designers should consider when creating interventions to support mood regulation. To address this gap, we conducted an exploratory case study focused on the “Sunday Blues”—a common dip in mood experienced at the end of the weekend as the new workweek approaches. We designed WeMo, a system aimed at helping users capture weekend highlights, culminating in a visual summary displayed on Monday. We engaged 15 participants in co-constructing stories around their potential use of the system. Participants expressed frustrations with the system’s features, concerns about its effectiveness, and obstacles to its application in daily life. Based on these insights, we highlight key considerations for designing mood-regulation interventions, such as balancing mood regulation with other fundamental needs, addressing the complex roots of mood, and respecting the acceptance of negative moods. By identifying user concerns and translating them into design considerations, this study provides actionable guidance for practitioners and contributes to the growing body of research in mood-focused design.