Kokoro"s school partners with another institution to organize a fair where they can trade or donate gently used household goods that people no longer need. The event aims to reduce waste and foster community spirit. While heading back from class, Tama Elder informs her that she and her Cocotama companions have earned a visit to the Cocotama World. There they witness how fully developed Cocotama deities operate, hoping to inspire a new appreciation for everyday treasures. Elder Tama requests Kokoro"s assistance in teaching people to appreciate the worth of their belongings instead of discarding them so readily. However, Tepple had slipped into the Cocotama realm with the others and stole a key acorn that opens the Happy Tree, which houses the Happy Stars—the source of their world"s magic. Elder Tama discovered it was gone and the Cocotama squad tries to recover it. He explains that mushrooms are sprouting on discarded items because they arise from sorrowful emotions, and they release negative energy that harms both humans and Cocotama. The Cocotama can eliminate them, but not without the acorn and not fast enough to keep up with how quickly humans are discarding things.
Tepple uses the acorn to seize a Happy Star, unintentionally creating a dark rift and spawning mushrooms throughout Cocotama World. The Happy Stars start leaking into the human realm, draining all its magic. Kokoro and the Cocotama must mend Tepple"s heart before darkness engulfs the human world. Only by restoring balance can the realms survive.
