The text on that spread page with the corpses towards the end says that "the boy made a choice", that "I won't commit suicide because of my bullying but instead I'll kill the one that bully me".
All in all it seems pretty interesting, The first chapter feels pretty slow but really sets the story in place with the two main characters. The series might branch out into supernatural later on but it's not totally confirmed yet.
Something I found really interested in the first chapter is the use of the '
2' with two main characters, the number comes back on important dates and months; is mentioned in all the cases of bullying told at the beginning where the victims are always either "two middle schoolers" etc and in my opinion it's also present in the title with '山羊座 - yagiza' with is most likely a reference to the Capricorn (late January to early February - February is the 2nd month of the year ans written 2月 in Japanese).