Kotarou is the protagonist of Rewrite. He is a high school student with a frivolous personality and is known to be arrogant. Though not fully realizing it himself, he meddles in the business of others, and as such tends to get easily drawn into incidents. The beginning of Rewrite centers around Kotarou's antics in his attempt to revive his school's Occult Club.

Spoiler

Kotarou suffered from an accident when he was young, which caused him to sustain brain damage and suffer from amnesia. Kotori managed to save him on the verge of death by implanting one of the Key's ribbons in his shoulder. Kotori believes she might have resurrected her childhood friend as a familiar, and she comments that his personality changed drastically after the incident. Other than his initial ability from birth to rewrite himself, which allows him to fundamentally change himself, such as gaining superhuman strength and senses, the Key's ribbon, gave Kotarou a second power, simply named "aurora", which is Kotarou's life force seeping from a wound in his right arm. It resembles a blade, but Kotarou finds other uses for it as well.

Spoiler

Kotarou was originally a member of Guardian, as shown in the Terra route. In every single timeline, he ended up attempting to kill Kagari due to his involvement with the group, which led to the incident where he was saved by Kotori implanting one of the Key's ribbons in his shoulder, but fell victim to amnesia. After this incident, he had stopped physically aging due to being part familiar, so he was able to fit in in school despite being ~10 years older than everyone else.