Chikyuu no Kodomo

A man and a woman are both hit and killed by a train. They are of different ages and genders, but they have one strange thing in common - their heads were crushed. Makoto, the brother of the dead man, and Hoshiichi, the son of the dead women, realise that there is a link between these mysterious deaths - they were not suicides, but murders, with a mysterious organisation involved. And what of the strange creatures also linked to the deaths?