Citizen Sleeper 2: Starward Vector

This is missable if you refuse to help Kadet or later refuse her offer to join your crew.

You first meet Kadet on Far Spindle after fully exploring the middle section of that place. Two days after your first encounter, she'll ask you for help retrieving a hidden encrypted data disk from her place, which has been hit by mercenaries who are apparently after that disk. Agree to do this and fill the action clock at her place. Don't worry, despite the narrative suggesting that the other guys are also searching for it, you aren't on a time limit and bad rolls only cause energy loss.

After you retrieve the disk, Kadet tells you a bit more about it (triggering the drive "investigate Hexport") and says she'll bring that disk to the workshop of a friend in the Scatteryards, who'll be able to break the encryption. She asks you to meet her there.

You can't actually get to the Scatteryards until you acquire a Haznav device to safely pass through fields of debris, which you'll automatically get after resolving the situation in Wellspring, where you search for Serafin's sister (unmissable part of the story).

After you have acquired that device, go to the Scatteryards and fully explore the place. You'll find Kadet at her friend's hidden workshop, but her friend who was supposed to break the encryption is missing, so you'll once again have to do all the work. (Fill an action clock by a series of either interface or intuit checks). On completion, you'll find out what's on the disk (which I won't spoiler here) and it makes Kadet want to explore the Hexport explosion site (which due to radiation can unfortunately only be reached from Darkside, so it'll still be a while until you can actually get there). She offers to join your crew in the meantime, which you should of course accept.

Doing this is also required for two more late game achievements that are tied to investigating Hexport ("brain scratch" and "stranger danger".)