The light beneath the ribs

The event happens in 2004, in Osaka

Akiko, a young math teacher, was on the shore, sitting down on the sand with the sphere of soul shining beneath her hands, she was looking at the sea before a boy named Setsuko disturbed his peace. He always wanted a sphere of soul, so he would always ask people with it. And his next victim was Akiko. At first she didn't want to help him, but after some pleading from Setsuko, she finally agreed. And that's where their journey begins. Would they find it, or will it end in a bad way?