When the Soul Hashira - Rei, was a Kinoe rank, he defeated a (former) Lower Moon 3 called Noru.

Rei had played with Noru - hitted by Noru's BDA and failing to attack him in purpose. After a hour of it, Rei cutted Noru's neck.

And Rei knew, Shinobu will be very mad, even Kanae tried to stop her.

Rei stayed lying on the floor, bleeding a lot. Until...the Class 1-A, plus Aizawa and Shinso, found him.

Tenya: "Sensei! Here's a person..."

Izuku: "Is he...dead...?!"

Bakugo: He smacks Izuku. "This is too bad wound that would get by villain's attack, Deku."

Then, some Kakushis arrived at the scene. The Kakushis thought the Class 1-A hurt Rei.

Goto: "H-HUH?! WHY YOU HURT HIM?!"

Rei: "They didn't..."

Kakushi: "D-don't move there, your wounds are bad!"