This paper explores the development of "We! Connect Cards," a card-based learning tool intended to support interpersonal relationships across various workplace and learning settings. The designed artifact is a card deck containing 60 cards with a question on the front and an action on the back. We discuss the development process of "We! Connect Cards" within the framework of a 5-phase design model. The purpose of our design paper is to share the design work of "We! Connect Cards" while exploring the utility of this model as a guide for creating and improving the design work. To understand the design case of "We! Connect Cards," we draw upon relevant Human-Centered Design literature and concepts with an introduction to the chosen design model developed by the Stanford University d.school. Three test cases of the "We! Connect Cards" were conducted in a nonprofit, corporate, and higher education context. We include the scholarly discourse on the value of supporting interpersonal relationship development to situate the reader to the intended use scenario and learning outcome of this card-based tool. We organize the paper by the three iterative cycles of design, each within a nonprofit, corporate, and higher education context, to highlight the valuable insights and fruitful failures of each formative test case.