“Who is the other person inside you?” The man in front of me was pointing at my stomach. Instinctively, I placed a hand over it. But there was nothing there. No pain either. “What are you talking about?” The man didn’t answer. He simply stared at my body with a puzzled expression. No. He was looking inside me. Until yesterday, the world had only had forward and backward. But now it was different. There was left and right. The ground had width. Buildings had shape. The world looked like a picture drawn on an enormous sheet of paper. The only thing missing was height. I was the same. My arms, my legs, my face— everything was flat. Seen from the side, I would probably look like nothing more than a single line. And in this world, even the inside of my body couldn’t be hidden. Everything beneath my skin was visible. My heart. My lungs. My blood vessels. My bones. It was as if a human anatomy model had been crushed flat, leaving my insides exposed. I felt sick and looked away. But the man was still staring at my stomach. “There.” “What’s there?” “A person.” He didn’t sound like he was joking. I looked down at my stomach. At first, I couldn’t see anything unusual. Between my organs was a dark shadow. I thought it was just a shadow. Then it moved. “What...?” A tiny face emerged from the darkness. It was a human face. A man who looked about my age. A face I had never seen before. He was staring at me from inside my body. I stumbled backward. “Who are you?” The moment I spoke, the man inside my stomach moved his lips too. But I couldn’t hear his voice. He was desperately trying to tell me something. I leaned closer. I watched his lips. Three syllables. Probably— “RUN.” Run. The next moment, my smartphone vibrated. The screen lit up on its own. DAY 2 DIMENSION: 2 Below that, a new message appeared. “OBSERVATION TARGET CONFIRMED” Observation target? More text followed. “INTERNAL ENTITY DETECTED” Internal entity. There was no question it meant the man inside me. “Wait.” “Who is this guy?” I asked the screen, but there was no response. Instead, numbers appeared. 00:59 00:58 00:57 A countdown. I had a bad feeling. “What happens when that reaches zero?” I asked the man in front of me. The expression vanished from his face. I looked around. The people of this world who had been walking along the street only moments ago had all stopped. And every one of them was staring at me. No. Not at me. They were staring inside me. “It found us,” the man whispered. “What did?” “The outside.” My heart jumped. The word I had answered with in yesterday’s world. The thing that didn’t exist there. “The outside.” Why was that word appearing here too? I looked at my smartphone. 00:31 The man inside my stomach was frantically trying to tell me something. This time, I could read his lips. “DON’T TRUST IT.” It? Who did he mean? The man in front of me? The people of this world? Or— the smartphone? 00:15 A new question appeared on the screen. “DELETE INTERNAL ENTITY?” Below it were two options. YES NO “Delete?” The man inside me shook his head. Desperately. But the man in front of me said, “You should erase him.” “Why?” “Because he isn’t you.” 00:09 I reached to press NO. At that moment, the man inside me suddenly reached toward me. From inside my flat body, his hand moved in an impossible direction. Toward this side. No. Toward the “outside.” His fingertips burst out of my stomach. The world shook. The buildings around us folded like paper. The people all screamed at once. “THREE DIMENSIONS!” 00:03 The man’s arm was extending out of my body. And suddenly, I understood. This man wasn’t inside me. We simply couldn’t perceive the world he existed in correctly. 00:02 00:01 I pressed NO. The screen turned completely white. “DELETION OF INTERNAL ENTITY REFUSED” “OBSERVATION ERROR” “DIMENSIONAL BOUNDARY DAMAGED” A black裂け目 opened beneath my feet. At that moment, for the first time, I heard the voice of the man inside me. “You can finally hear me.” The moment I heard it, I froze. A face I didn’t recognize. A body I didn’t recognize. And yet, I knew that voice. It was my own. The world began to collapse. One final message appeared on my smartphone. DAY 3 DIMENSION: 3 And beneath it, a line that had never appeared before was added. “ORIGINAL: 2”