Neither do I but it feels more like an experience than something you're supposed to understand
As far as I can tell - they meant to summon the ghost of the girl who may or may not have died due to bullying, but instead summoned another spirit (?) who fulfills a wish in return for taking a life in return. They never realised that's what they'd done, and the spirit randomly killed a creature on the outside (probably a bird) the first time, and Hayami intervened and offered it a flower to placate it when it was asking for another, therefore preventing it from taking the life of one of the students as its toll.