#specifically the underworld here is based on annwn but like. very loosely. for flavour.

[alternis]

actually i think maybe the funniest way to reveal river's secret (even to him) backstory would be to have it entirely revealed in a world-without-YJ-esque plotline where him and his teammates are shoved into a reality bubble where they never became heroes and everybody else is having like conventional "never got super powers" or "never took the step to use their powers to help people" plotlines and struggling against the magical being that trapped and brainwashed them.

meanwhile river is fighting for his fucking life in not-skartaris because in this world his mother wasnt able to take him from the otherworld to the human world to hide. so he never got experimented on and didnt get his cat-traits, and bc he was never under the glamour that hid him as a human there's a good chance the theoretical reader literally would not recognise him at first bc even his childhood flashbacks have been him in his human-mode.

the reader finally finds out why his mother tried so hard to hide river in the human realm and unless they've put the Clues together they dont even know it's him, he's written and presented as a new character who's part of the overarching plotline with the magical villain bc most of river's "never became a hero" plot is happening in the background and seems like worldbuilding. then the rest of the other characters all converge on the underworld and hey this background character just became a foreground character very quickly as all the dominos that river had been setting up in the background have revealed themselves to be Foreshadowing and have resulted in the villain's plot getting completely derailed. one of their teammates has just realised that alt-river's name is literally a translation of the word 'river' and is super embarrassed it took them this long.