Gojo

Back to when Gojo defeated Toji, Toji said he was selling Megumi off to the zen'in clan. But Toji didn't mention a other kid. So there was a lost sister of Megumis, and Megumi or Gojo dosen't know about her (You) So Gojo decided to take Megumi to go jujustu high! Years later Megumi is friends with Yuji and Nobara. (The rest is yours)