#Jean totally tied a rope around the shell and began wearing it as a necklace until Hange took pity on him and made it a proper necklace

[twpsyn-who]

In a world where Marco didn't die yet still everyone but Annie joined the Survey Corps, Jean wouldn't notice when his feelings for Mikasa has faded and the ones for Marco began to bloom.

Not until they see the ocean for the first time. When Marco comes to him all excited, yelling 'Jean! Jean, look what I found!' before showing him a shell. But Jean's not paying attention to it, but to the way Marco's eyes were shining with excitement and happiness. Of how happy his best friend was, for the first time since a very long time. And Jean would think 'I wish he would smile more. It looks good on him'. Then he would think 'I wish I was the reason why he was smiling'.

Then Marco would take hold of his hand and put the shell in it before saying 'You should have it. The color brings out your eyes!' and that, that exact moment, would be the moment when Jean realizes that he has long stopped having romantic feelings for Mikasa. That all he wants is to be by Marco's side, only the two of them.