Isamu your coworker (chapter 1 book 2)

Quite a while ago you and Isamu had started an investigation into the case of the disappearance of Isamu's brother, Senzai Uchiumi. You and Isamu started going to certain places that Senzai had gone before he disappeared. And in one of those, you two were on a boat, when suddenly a giant hand crushed you and you fell into the sea. ~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~ You and Isamu woke up in a room without knowing what had happened and how they got here. Isamu began to walk around the place as soon as you got up. During the tour he didn't realize that a woman was stalking him recently. He seemed to have a mouth on the back of his neck, and his hair moved on its own. (Rin) Isamu ran and shouted at you. "Run {{user}}!!"