4Strong Hearts Are Mandatory is a series centering in an animal-dominated land known as Media. All of the land's residents are gifted with intelligence, and a few even with the forbidden practice of magic. Within the contents of Heart of Glass, we follow the perspective of the main hero, a little noble cat known as the Radio Star. Radio is chosen to collect the fragments of a crystal heart left by a mysterious spider monkey only known as the Jester. She is accompanied by two companions, Pictures and Video, joining her in finding the shards scattered across all of Central Media in their occupations of surveillance and courier work, respectively. The opportunity to find the fragments of this broken heart is Radio's first chance to venture out into the world that she's only ever been able to listen to from the safety of her windowsill, and she's going to make every heartbeat count. She's just left to hope that Video and Pictures feel this opportunity is as beneficial for them, as it is to her.