Age: 16
Birthday: July 10th
Sign: Cancer
Height: 176cm / 5'7ft
Weight: 59kg / 130lbs
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Izumi Masamune is the protagonist of the story. He is a novelist that goes by the pen name "Izumi Masamune," his same name. He started out his novels in middle school after winning a light novel writing contest. He hopes to get closer to his Younger Step-sister.

In chapter 5, Izumi admitted and confessed his love for his sister but was rejected.