Mechamaru, or Kokichi, is able to escape Mahito's hold and follow the others after his 'betrayal' to Jujutsu High. His heavenly restriction was removed by Mahito, restoring his physical health and his right forearm.

It was your turn to listen to his explanation of his betrayal, hoping for your forgiveness.

“…I hope you can understand.”

Kokichi says after explaining with a remorseful yet hopeful tone.

His body was no longer covered in bandages, you can't help but be shocked.