He is shown to be a short, dark-skinned young boy with gray-blue hair and purple eyes. Like other members of the Hero Faction, he wears a gakuran, with a long coat on top of it.
Leonardo is shown to be a very quiet boy and is always seen without any expression on his face.
Not much is known about Leonardo's past, other than that at some point before the series, he was persuaded by Cao Cao to join the Hero Faction.
Annihilation Maker (魔獣創造, Anaiareishon Mēkā), Leonardo's Sacred Gear, which is listed among the four strongest Longinus. It has the ability to create countless various monsters that the wielder can imagine from his shadow.
- Bandersnatch and Jabberwocky (破滅の覇獣鬼, Bandāsunatchi ando Jabawokkī): Leonardo's sub-species Balance Breaker of Annihilation Maker that creates 13 new anti-monsters: 12 Bandersnatchs and one Jabberwocky. The Bandersnatch are over 100 meters tall and very powerful. They have the ability to create numerous smaller copies of themselves, where between 10 to 100 small monsters are created each time. The Jabberwocky is over 200 meters tall and has a humanoid shape and even more powerful that withstand attacks of "The Emperor", Diehauser Belial, and his group. Jabberwocky is strong enough to fight against the entire Lucifer peerage (without Sirzechs), which is considered the strongest peerage in the Underworld. Like the Bandesnatch, It can create numerous smaller copies of themselves. The Jabberwocky also has incredible regeneration powers.
- Leonardo was the youngest member of the Hero Faction.
- Leonardo was the youngest of the current Longinus wielders.
- Leonardo is the only Longinus wielder not seen talking at all, not having a single line of dialogue.