I Had That Same Dream Again by Yoru Sumino

An unhappy girl who engages in self-harm, a woman ostracized by society, and an old woman looking to live out her twilight years in peace―what could three such different people have in common? That’s what grade schooler Koyanagi Nanoka is trying to find out. Assigned by her teacher to define what “happiness” means to her, Nanoka sets out to get to know these three strangers―and through them, perhaps, to know herself too.