Skein

This story probably doesn't exist in the same world as the others, but I'm listing it here because of common themes.

Skein is the story of a superhuman assassin created to deal with out-of-control super soldiers in a twenty-minutes-into-the-future dystopia.

The narrator is Kyle, who has met up with Todd 4 times at sleazy bars before the story starts, and realised that Todd was almost a different person each time.

Todd's training was slightly unusual, in an attempt to ensure he's not capable of rebelling against the corporation that owns him. There's a time machine implanted at the root of his brain, which is responsible for transmitting the majority of his neural impulses through time. Essentially his soul and self-image travel back and forward in time in an unpredictable pattern, causing him to experience the days of his life in random order. Like a tangled ball of string, or the pages of a books that's been dropped and put back together wrong before collating. His childhood was mostly taken up with advanced military training, where his much-more-experienced mind could drill his body in the correct movements and gain the muscle memory he needed without needing to wait for him to grow up properly. This meant that he was able to fight effectively as young as his early teens. At some point later in life he becomes a scared child who hasn't learned what's happening yet. When he feels his child persona coming on, he will attempt to hide somewhere he won't be found. If he is, the result is often violence. Because he doesn't know what's going on, he's scared, he has all the mental development of a child, but the muscle memory and reflexes of an elite killer.