The Masques anonymity story.

Each Masques user has exactly one Masques ID (Mid).

A Mid consists of two public keys (identity for Masques, destination for I2P) and a little meta data (including the user name).

Having possession of someone's Mid is what allows a user to send them a friend request. Mids can be sent as QR codes or plain text. A Mid sticks with you, and is what connects you to your friends.

Details here:

At least in v1.0, there will only be one Mid per user. The user may change their user name, but they may not change their Mid.

If it is important to protect your anonymity, you probably want to create a separate Masques account (which gives you a new Mid) that you are uber-careful with.