Soma is a dead body that is brought back alive using a forbidden technique and become a zombie who follow their master order.
During all of her life, Rinka was imprisoned by her father in her room and only accompanied by her father's soma, Yan-yan, as her caretaker. She always wanted to go outside and searched for Hourai, a place where fishes is swimming in the sky, birds flying in the water and waterfall go up to a higher ground.
One day, she couldn't wait anymore and with Yan-yan's help they escaped from the room and went outside. And then, their journey to find Hourai begin.