"Hello, detective. I have a request for you."
The letter you received from Japan, started like this.
The letter was written by a girl named Erika.
Deciphering the code which her father left for her, was the request made for you.
While you unlock the code, Erika will travel all around Tokyo city, of course with you, through the internet.
What is the hidden treasure, and why did her father leave the codes behind for her? Why Tokyo city?
...This story is about you and Erika, and her mysterious secret letter.