Can't remember name to a manga?

I remember the first chapter a little, but I can't remeber the name! There was an older boy who could somehow talk to dead people (I remember him talking to this little girl at the park). One day, he's attacked by a monster from the dead (it's huge and looks sort of like a spider-thing). An older girl jumps of nowhere and kills the monster with a special sword. She explains some stuff and then leaves. The next day, he finds her in his class. That's all I remember. I know it sounds weird but if you know the name please tell me. Thanks!