Secrets abound in "Lyra's Magnum Opus". Tetsu is keeping the fact that he is bisexual and non-binary from everyone in his life. The whole series is about his journey to reveal it on his own terms and becoming comfortable with these things himself. He is semi-famous in the book's world as a musician and dancer from the start, so he's also keeping it from the world. Sana's band, Lyra, has long kept secret from the music industry that Sana (their singer) has a degenerative illness that is later revealed to be terminal in actual fact, which is the other shoe dropping that most of the band didn't even know. The whole series is about Sana revealing this on his own terms to their fans and the whole world as the band becomes more famous due to their unique situation and new association with Tetsu who is already famous as the drag queen Aurelia. It is also kept secret for a while that Tetsu and Sana are together, and Tetsu gets fired from his management company for being queer due to them finding out about this relationship pretty early on. The slow reveal that Tetsu and Sana are dating and then married is also a major theme in the book (it kinda gets more cute, though, this particular secret, as their mutual fans adore them both as they watch their journey).