Ethan!!!

Riku's battle stance pre vs post injury support this theory as well so I brought it up with your post;

Pre-injury stance: wrist twisted and facing upwards in an offensive stance; uses that arm to dodge by acrobatics and front flips

Post injury: wrist facing down, hand in a more neutral position; stops using acrobatics as a means of dodging attacks

The biggest thing that I personally think supports this is that DDD would count as his Pre-injury body, and for a brief period of time he goes right back to the wrist twisted position. By the time kingdom hearts 3 takes place (which is canonically close in time to DDD) he goes right back to his post-injury stance. Almost as if pre-injury is the preferred stance, but not able to be done anymore.

And all of these observations are consistent with the hand that got hit guarding during their fight;

It wouldn't be the first time Square and Nomura have put an injury that was never mentioned or spoken about beside audience observation either; the most notable I can think of is Noctis, who is shown in a wheelchair as a child, and when running for periods of time as an adult has a slight limp to his run animation.

One more funky thing someone on twitter pointed out in the thread was that in his battle against Roxas, Riku adopts NEITHER of his known battle stances, instead keeping his hand completely neutral and by his side. Which I just thought was neat;

Games Sephiroth and Genesis are banned from playing + why

*not a vlog because I had this post in my drafts but saw this question and decided to answer with it I'M SORRY*

Tic-tac-toe - Banned because one time Sephiroth won four times in a row, Genesis got so angry he punched him in the face.

Monopoly - ALWAYS ends in tears and screaming. One time another SOLDIER on their floor called security to Angeal's apartment because he thought someone was getting murdered. It ended up being Angeal, who lost his cool, then threw the board off the table and simultaneously angered Gen, Seph and Zack.

Rock, paper, scissors - One time Sephiroth threw scissors against Genesis's paper and Genesis punched him in the face.

Chess - banned by Lazard, who once walked in on Genesis trying to do the heimlich maneuver on Sephiroth, who accidentally swallowed a chess piece.

Tag - One time Sephiroth tagged Genesis so hard he accidentally threw him down a flight of stairs.

Snakes and ladders - Sephiroth had never heard of snakes and ladders before, thought it involved actual snakes and ladders. It took an entire day to locate all the snakes loose in the ShinRa tower. To this day no one knows how Sephiroth acquired live snakes.

Co-op video games - SOMEONE punched a hole through Angeal's TV and to this day neither of them will admit who did it (it was Sephiroth).

Hide and seek - They once played with Angeal, Zack and Kunsel. Neither Sephiroth nor Genesis could accept defeat so they simply didn't come out of their hiding spots. It took a 48 hour manhunt to locate the two SOLDIERs.