The rain had been pouring for days, casting a gloomy veil over the once bustling streets. Professor Allen stood by the window of his cramped office, watching the droplets slide down the pane like teardrops. His latest project, a novel based on the enigmatic letters of his neighbor, Miss Katsuragi, was taking shape. But there was something that didn’t add up.

He couldn’t explain it, but those letters… they seemed almost… real. The way she wrote of her thoughts, her feelings, it was as if she was speaking directly to him. But the catch was, she was long gone. And yet, the letters kept coming.

Allen’s eyes widened as he began to piece together the mysterious puzzle. Who was Miss Katsuragi, really? Was she what she seemed? Or was there something more to her identity? The lines blurred as his imagination ran wild.

With each new discovery, Allen became more obsessed. He stopped seeing his friends, his family, his colleagues. The only thing that mattered was unraveling the tangled threads of Miss Katsuragi’s life. But as he delved deeper, the more questions he found himself asking.

Was she his guardian angel, guiding him through the darkness? Or was she a mere figment of his imagination, born from his own psychologically complex psyche? The Mysterious Girlfriend had become his reality, a world where nothing was what it seemed.

And Allen, sitting in his office, was just a pawn in her game.

The rain, once a soothing melody, had become a merciless drumbeat, echoing the pounding of his heart. He knew then that he would never be able to escape the web of secrets, woven around the enigmatic figure he was convinced was real – his mysterious girlfriend.