One Day a Message Window Appeared Out of Nowhere!?

The protagonist, a university student named Kazuya Hayakawa woke up one day with a message window that shows up in his field of view. This window is always visible to him, and when certain lines are displayed in it, he gets thrown into confusion.

From that day onward began Hayakawa's daily ordeal of getting manipulated by this message window.

(Source: Amazon JP)