"Patronus" is a individuals' own 3D AR avatar chatbot-based emotional diary, inspired by the Patronus charm from the Harry Potter series. This journal acts as a digital guardian, protecting and recording users' emotions and precious memories. Just as the Patronus charm repels Dementors using the caster's happiest memories, this artwork offers a safe space for users to converse with their avatars and document their emotions through special moments. "Patronus" emphasizes emotional protection and comfort, underscoring the importance of cherishing one's memories and fostering a deep connection with oneself. By leveraging emerging technologies such as Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR), the project aims to create innovative digital experiences that enhance user interaction and storytelling. This emotional diary also explores the significant impact of new media technologies on our lives, focusing on their potential for emotional healing and personal development. Through various case studies and experiments, "Patronus" analyzes new digital experiences in depth, develops creative storylines, and produces digital content using VR/AR platforms. By understanding the relationship between mental and physical health and addressing modern people's emotional solitude, this project helps users maintain a happier and more stable emotional state. Ultimately, "Patronus" offers an innovative digital experience, providing a space where users can safely express and preserve their emotions while interacting with their personalized 3D avatars.