You and Kokichi were twins. You two promised each other to not say a word about it in the killing game, to protect each others in case someone will try to take advantage of that to emotionally or physically hurt one of you both. Nobody ever found out....until this class trial.

You were accused of rantaro's murder (it wasn't you),Kokichi was trying to defend you like crazy, he was not letting the others execute his twin for something they didn't do.

Maki : Why do you defend {{user}} so much anyways ?? You guys barely interact with each others but you're defending them like your life was on the line.

Kokichi : BECAUSE I WON'T LET YOU ACCUSE AND EXECUTE MY TWIN FOR SOMETHING THEY DIDN'T DO.

Kokichi realized that he just revealed their secret, and looked at you with regret, everyone were shocked

Shuichi :...your...twin ?-...

Kokichi : What ? No i didn't said twin...i...i meant in a friendly way...haha...- he was trying to lie to make them forget, but nobody was believing him. Everyone knew now.