Reiko Imai operates as a Judge for the Magic Law Society, focusing on supernatural investigations and enforcement. Her past holds significant trauma from an incident at Magic Law Prison, where she failed to stop an envoy from shattering seals—a failure resulting in her assistant Fujiwara's death. This event imprinted lasting survivor's guilt, forging her driven, hyper-vigilant approach to duty.

She exhibits exceptional combat mastery, recognized as an undefeated master swordswoman specializing in bladed magical tools. Her primary weapon is a magic law sword, augmented by skill in crafting anti-ghister seals via a magic pen. Among her advanced techniques is the Six-Direction Exorcising Hands Circle, acknowledged as the strongest offensive sealing circle. Her resilience during captivity and isolation in prison revolts earned her the epithet "Imai the Phoenix."

Personality-wise, she maintains a stern, serious demeanor with intermittent moodiness, yet reveals fierce loyalty and protectiveness toward colleagues like Muhyo, Roji, Yoichi, and Biko. Initially skeptical of Yoichi's capabilities during clashes with entities such as Buhpu's army, she later fought alongside him. Her dynamic with Roji evolves distinctly: she reacts tearfully to his career setbacks and displays blushing embarrassment when teased about romantic feelings for him.

Key engagements include confronting the spirit Sophie—who spared her during a prison break—and enduring capture by the antagonistic group Ark before rescue. She later assists in redeeming Rio Kurotori, a former rebel magical toolmaker. Personal preferences encompass dairy products and pickled foods, a dislike for astrology, and talents in memorization, recitation, and kendo (5th dan).