I Was Observed Morbidly by Her

(Isolation-induced yandere + first-person male protagonist + slow heat) High school student Haruto Sato is used to being alone. Until Misaki Amami appeared - she was only gentle to him, only smiled at him, and only blushed in front of him. Her world was so small that it could only accommodate him. What he didn't know was that those friends who disappeared, those troubles that "happened" to be solved, and those things that made his world smaller and smaller were all arranged by her. In a systematic way, she cut off everyone around him. She is the cutter of "Targets" No. 1-23. He is No. 0 And No. 24 - "Always stay with me."