Kotetsu Izumi

Kotetsu is portrayed as a caring father who takes Masamune Izumi's interests seriously. Rather than dismissing his son's desire to write professionally because of his age, he listens to him and becomes part of the family environment in which Masamune begins pursuing that goal.

His family relationships also suggest an affectionate and dependable disposition. He maintains a close relationship with his younger sister Kyouka Izumi, while his remarriage creates the blended household shared by Masamune and Sagiri Izumi.

The series gives Kotetsu relatively little direct screen time, with much of what is established about him coming through flashbacks and the memories of his family.

Kotetsu has no supernatural abilities or combat powers. Eromanga Sensei depicts him as an ordinary adult, and the story does not establish specialized physical abilities or techniques for him.

He is familiar with light novels and supports Masamune Izumi's interest in writing. In the anime, he is shown reading light novels himself, providing additional context for the household in which Masamune develops his enthusiasm for the medium.

Kotetsu is Masamune Izumi's biological father. After the loss of Masamune's mother, he eventually marries Sagiri Izumi's mother, making Sagiri his stepdaughter and bringing the two children together as a family.

Flashbacks show Kotetsu during Masamune's early development as a writer. He is present when his son declares his intention to become a professional author, connecting him directly to the beginnings of Masamune's light novel career.

Kotetsu and Sagiri's mother later die in an accident while on their honeymoon. Their deaths leave Masamune and Sagiri without their parents and contribute directly to the household circumstances at the beginning of the main story. Kyouka subsequently becomes the siblings' legal guardian while allowing them to continue living together under agreed conditions.

Masamune Izumi is Kotetsu's biological son. Kotetsu supports his interest in light novels and is present during the period when Masamune decides to pursue professional writing. Masamune continues to remember and miss his father after his death, even as he accepts responsibility for maintaining the household he once shared with him.

Sagiri Izumi becomes Kotetsu's stepdaughter after he marries her mother. The marriage also makes Sagiri and Masamune Izumi stepsiblings and establishes the blended Izumi household central to the series.

Kyouka Izumi is Kotetsu's younger sister and Masamune Izumi's aunt. Following Kotetsu's death, she becomes the guardian responsible for Masamune and Sagiri.