Tsukasa is an Alpha through the whole main story. It doesn't say he chooses to become an Omega. That bonus chapter is basically what things would be like if he became an Omega. It was your choice to read/acknowledge it.
Tsukasa is an Alpha through the whole main story. It doesn't say he chooses to become an Omega. That bonus chapter is basically what things would be like if he became an Omega. It was your choice to read/acknowledge it.