乃木坂46メッセージ is a lifestyle app developed by Sony Music Solutions Inc. exclusively for iPhone users. This free app allows fans of the popular Japanese idol group, Nogizaka46, to subscribe to their favorite members and receive exclusive messages, including text, photos, and videos that can only be seen within the app.

One of the main features of the app is the "Talk" function, which is a monthly subscription service. Subscribers can receive messages from their favorite members, and even send fan letters (letter service is a paid feature) to them. The app provides templates for both card-style and letter-style messages, allowing users to choose the format that best suits their message.

It's important to note that fan letters sent through the app are private and cannot be viewed by other users, ensuring the privacy and security of the communication.