Leo Regulus (獅子座（レオ）のレグルス, Reo no Regurusu) is the Leo Gold Saint in Lost Canvas.
Protect the Ship of Hope
Once in Tibet Himalaya, he meets his old sparring partner Yato, and the other Bronze Saints. Being practically a novice in terms of culture, he is confused by the work and effort of Bronze Saints in repairing the boat.
Regulus used his technique to destroy the ice that surrounded the Ship of Hope, that will be used by Athena to reach the Lost Canvas. The attack was so quick, that the Bronze Saints couldn't see it when it was performed. He engages into a fight with Behemoth Violate, overcoming her tremendous strength two times, the first one when he concentrates his Cosmo in his finger tip, to stop the attack of the Specter. The second time, when he discovers the truth behind Violate's shadow technique, avoiding the attack of the dead, and making them attack her own controller. At the end of the fight, Leo simply fulminates Violate with his Lightning Plasma. From the view of his opponent, he would see himself trapped in a net formed by rays of light, which are the traces left by his fist. After his battle with Violate he was struck by surprise by Aiacos and was retrieved by Yuzuriha. He has been seen reuniting with Athena's army in heaven and together with Sisyphos and Shion he opened the gate to the Lost Canvas with the Athena Exclamation.
Entrance to the Demon Temple
There he survived the voyage through the clouds which turned all non-Gold Saints (except Pegasus) into stone and arrived at the Second Demon Temple, along Shion and Tenma, where he was ensnared by Balron Rune's whip, being freed thereafter by the Aries Saint, thus proceeding to the next Temple.
Regulus v.s Rhadamanthys
He was shown arriving to the Saturnus Temple, preparing to engage in battle. Regulus attacks the Wyvern along with Tenma, only to have their attacks negated by the Specter. After the defeat of Partita, Regulus encounters Wyvern in the Saturnus Temple and after studying his physique and technique, Leo locks himself in combat against the Specter, vowing to surpass his power. Furious for revenge, Regulus reveals then to the Wyvern, that he is the son of Leo Ilias, the man who broke off his horn. Regulus reminisces about the quiet life he shared in the past with his father Ilias and engages the Specter without restrain. As Wyvern has attained divinity, Regulus is in clear disadvantage, expecting to revert the situation, he performs the devastating Athena Exclamation unassisted, which he learned from his mentor Sisyphos. The Wyvern effortlessly negates the attack of the Leo, who then resorts to summon the power of the twelve constellations and combines them into a single attack, releasing it as a concentrated shockwave known as the Zodiac Clamation. Regulus is consumed by the explosion, which the Wyvern survives unscathed. Having become an incorporeal entity, Regulus attacks the Specter once again, with the potent Lightning Bolt. Having inflicted his final attack on the Specter, and fulfilled his destiny as a Saint, Regulus rejoins his father in the afterlife.
A tactical genius, he is able to adapt to any situation in combat quickly, observing the capabilities of the opponent.
- A major strength of this is the ability to learn the skills of the opponent which is capable of decoding techniques. This allows Regulus to manipulate the opponent's techniques against their will and perform them as well.
- Possessing a great power and strength even among the Gold Saints, being able to perform techniques that could defeat a judge from Hades's army of specters in a single attack, and resist enough to survive the attack of Aiacos Garuda, and still support in the making of another Athena Exclamation, which he survived the explosion.
- The ability to become one with the World or Nature, a strange state where Regulus is able to return despite being faded out of existence by the Zodiac Clamation. In this state he loses all traces of presence, in the words of Radamanthys "he was like the wind", his power was greatly increased allowing him to penetrate the defense of Radamanthys, something that even powerful techniques such as Athena Exclamation or Zodiac Clamation couldn't perform. It is unclear whether it was speed or something about this new state, but even someone on Radamanthys enhanced divine level could not be able to dodge his attacks nor fight back.
- Lightning Plasma (ライトニングプラズマ, Raitoningu Purazuma): Regulus focuses and releases his Cosmo in a series of small electric light beams, that attack the opponent at the speed of light. Unlike Lightning Bolt, it's impossible to see through several thousand punches launched instantaneously, as the enemy sees himself trapped in a destructive net of beams.
- Lightning Bolt (ライトニングボルト, Raitoningu Boruto): The Leo Saint throws his fist at extreme speeds, creating a rift in the air through which he forces a high electric current generated by his Cosmo. That continues to attack the opponent even if it's destructive force is held.
- Athena Exclamation (アテナエクスクラメーション, Atena Ekusukuramēshon): Although Athena Exclamation traditionally requires the combined Cosmos of three Gold Saints, in Lost Canvas, Regulus was able to cast it by himself after using it together with Aries Shion and Sagittarius Sisyphus. Such is the talent of Regulus, who surpasses all that his eyes observe. Since doing so did not break the Saints' code of one on one battles, he retained his honor when fighting against Wyvern Rhadamanthys.
- Zodiac Clamation (ゾディアッククラメーション, Zodiakku Kuramēshon): In Lost Canvas, Regulus exceeded even the power of Athena Exclamation when he revealed this cataclysmic ultimate move. It calls upon the constellations of the zodiac to launch the attacks of all twelve Gold Saints at the same time. He had watched their moves while training alongside them in the Sanctuary, and unleashed them on the divinely empowered Wyvern Rhadamanthys to teach him the true strength of humanity.
- Lightning Crown (獅子の大鎌（ライトニングクラウン）, Raitoningu Kuraun)