Some game spoilers for those who haven't played Half Life btw
This is the Adhesion AU!!!
Essentially when in Black Mesa, The G-man had to have his own measures taken when his employers didn't want him to save Alyx, so he placed a miniscule part of himself in Alyx to ensure that she stays alive. What he didn't know is that it would grow some sort of connection between the two of them that was dormant until Alyx 'saved' him from the vault because she 'repaid' it back.
This is extremely rare and he hadn't paid no attention to it until it was way too late, and so now they are bonded for life. If one dies, the other does too except if it's a natural death. This also makes Alyx slightly inter-dimensional as she has access towards some parts of his brain and vice-versa.
This of course leads to complications and strange business since this makes Alyx an anomaly among the G-Mans employers. She's now a spectacle, but also the bond genuinely can jeopardize the G-Mans job as they can also form subconscious feelings of affection, safety towards both subjects. So the employers could transfer him to another project and replace him.
Thats mostly all I can think of for now.
Feel free to add onto it with questions or ideas :)
Will probably doodle them later too.
(this au is totally not me projecting. i love strange uncle-like figures with their nieces)
