Yoru no Kurage wa Oyogenai, also known as Jellyfish Can't Swim in the Night, follows Mahiru Kouzuki, a gifted young artist who gave up on drawing after elementary school classmates mocked the colorful jellyfish mural she created. The hurt lingers for years, leaving her separated from the passion that once came so naturally to her. Her life starts to shift when she meets Kano Yamanouchi, a former idol with a troubled past and a dream she refuses to abandon.
When Mahiru is asked to design the mascot for Kano's new music project, JELEE, she takes a first step back toward the creative world she left behind. To help turn the project into something real, she asks her childhood friend and professional streamer Kiui Watase to assist with JELEE's first music video. The circle widens with Kim Anouk Mei Takanashi, a pianist and devoted fan of Kano's work as an idol, and together the girls begin chasing the goal of making JELEE a global hit.
As their collaboration deepens, each of them must face insecurity, disappointment, and the burdens that have followed them for years, learning how to move forward without letting the past decide who they can become.