Ikumi Oze is a major protagonist during the first half of the anime, but after becoming the fourth captain of the Ryvius he became the main and final antagonist of the anime Infinite Ryvius.
At first, Ikumi Oze was an easygoing and good-humored nature person who would never kill anyone under any circumstances even the other ship captains that were trying to kill him and the other children within the Ryvius.
Ikumi Oze harbored a dark secret that the others are unaware of, years before going into the Liebe Delta space program. Ikumi and his sister fell in love with each other. The society he lived in forbade incest. after knowing they will never be together Ikumi sister committed suicide, Such a traumatic event incident left Ikumi mentally unstable, and he became obsessed with protecting the lives of other people so he will never be forced to experience the pain of loss again.
After Akumi's girlfriend, Kozue Izumi was attacked, beaten and left mentally broken by a gang of bullies. Ikumi reached his breaking point and he fed up with the increasing amount of violence aboard Ryvius. Ikumi became a cold leader obsessed with keeping the Ryvius peaceful to the point he is willing to kill others that go against his ideals even his best friend or execute people for committing the smallest crimes like not doing their work " said the small problems now, can become big problems tomorrow" to justify his actions.