In 'Whose Diary Is It Anyway?', players assume the role of a quirky amateur detective who stumbles upon a mysterious diary in a bustling metropolitan library. As they delve into the diary's pages, they realize it's filled with foreboding entries about various unsuspecting patrons, all forecasting future events tied to their lives. With each entry, players must interact with the library's eccentric staff and a colorful cast of characters to piece together the web of secrets and uncover the diary's original owner before it's too late. As choices are made, the story unfolds in unexpected directions, leading to multiple endings based on the truths uncovered and relationships developed throughout the game.