Leo is the lively and blundering twin brother of Luna. He plays a "Morphtronic" deck, with transforming monsters that have different abilities in attack and defense position, and his key card is Power Tool Dragon. He idolizes both Yusei and Jack and is always looking after his sister Luna. During a life-or-death battle against Aporia, Leo's desire to protect Luna makes him the sixth and final Signer, with the Mark of the Crimson Dragon's Heart. He also comes into possession of the true form of Power Tool Dragon, Life Stream Dragon, which is also a Synchro Tuner monster which Yusei can use to summon out his strongest monster, Shooting Quasar Dragon.
- Leo and Luna's last names in fan-fiction are Javelins.