Read about the details and his personality here

Ruby is the mage that was once a regular boy without magical powers. While doing chores in the school library, his head was hit by a bookshelf. Shadow creatures appeared around this time to help him by handing a suspicious arrangement. After Owari's agreement, he changed in his looks - With this magic he got a peculiar curse. His hair and eye color changed into red without the ability to dye over, and after this, he changed his name into "Ruby". He still experiences obnoxious pain in the head and decline in his recollection of the past. So as not to experience consistent memory loss, he has to write everything down in the notebook and read it to remember important things. Shadows are trying to control him in every step he's doing. They know - Ruby should repay all sins of his past lives.

While being a student, Ruby is very curious and gets hyped when he sees a magical creature which he can study.