Lee Soleil is the rooster familiar partnered exclusively with Beast Knight Subaru Hoshikawa. He appears as a white chicken marked by a vivid red comb and wattle.

Lee Soleil possesses an explosive temper and aggressive nature, frequently voicing his opinions in loud, unrestrained outbursts. This habit consistently embarrasses Subaru, who often silences him. He exhibits fierce protectiveness over Subaru, viewing the knight with paternal devotion as if she were his daughter. This fuels his overt hostility toward Shinonome Mikazuki, stemming directly from Mikazuki's connection to Subaru.

Functionally, Lee Soleil operates as one of several familiars aiding the Beast Knights in their battle against the forces endangering Earth.