Margaret Corner, sister
Michael was a seventh year Ravenclaw during Dumbledore's Army and the Year of Darkness, and he is second lieutenant to Terry Boot. Mike died during the Battle of Hogwarts, and was the first casualty. Terry and Mike were cremated and their parents mixed their ashes and each took half of the boys' ashes, burying the ashes on opposite ends of England, with identical grave-markers.
Mike's mum, Elaine, wasn't supposed to be able to have children, due to injuries received during the First War, so Michael is a miracle to his parents. He does not get along well with his older sister (who is adopted), because she resents him quite a lot because she feels pushed to the side since the Corners had their "miracle baby", something Mike always felt guilty over. He was best friends with Terry. They had a Legilimency connection, and Mike felt that Terry was the only person who saw past his pretty face and saw him as another human being.
Michael attended the Yule ball with Li Su.
After Neville and Ernie are punished in the place of Luna and Hannah, Michael swears that is anyone is punished like that again, he will sneak out in the middle of the night and unchain them to help them.
This does end up happening when Elliot stabs Snape and is whipped in the great hall. Michael unchains him in the middle of the night and gets Elliot to safety off school grounds by using a corporeal patronus and side-along apparition.
Michael did not know Snape was following him and saw him do this so afterwards, Michael is chained up in the great hall and tortured by Professor Belsen.