It doesn't. Getting back works the same as getting here: Out of your control, and when you least expect it. Some people come and go, others seem to be stuck.

[ he's stuck. for now. don't ask him how he knows this. mamoru can't explain his abilities to anyone in spite of how freely some on this ship seem to be showcasing their own. it was different when you were a legit superhero in your own world with a secret identity to protect, nevermind the past life that made him so much more than just a seventeen-year-old with psychic powers. ]