Kaze no Wa ・Toki no Wa・ Suna no Kan

Synopsis

Akira is a special kid. Instead of going out to play like any other kids, he prefers to read difficult books for grown ups. However, his parents are deeply concerned about him. It's true that he can solve college level questions, but no matter what...he won't talk. What Akira's parents don't know is that Akira is being stalked by a mysterious man that only he can see. That man dressed in unusual clothes and shows up everywhere, even in Akira's room, especially when the subject of god comes to his mind. Akira is severely scared of this man and thinks that if he opens his mouth to talk, that mysterious figure will get inside his mouth and take over his body. Akira remains silent for years until an incident that triggers him to screams out for help loudly. Since then, that mysterious man never shows up again and his ability to solve difficult puzzles has gone too. Since then, Akira lives his life like nothing happened until one day he's asked about his belief in god. While he gives out his answer, to his horror, he spots that mysterious man again. (Source: Anilist, edited)