The Leone di Cieli ver. Vongola was created by remodeling a Leone di Cieli with the Vongola's latest technology. Its figure is that of a small lion cub that acts like its master in and out of battle, going from a serious, powerful animal to a timid, easily frightened cub. As they are both based on the same Box Animal, Natsu has some similarities to Xanxus's Ligre Tempesta di Cieli.
It was first opened incorrectly and appeared in a monstrous shape, a mirror of Tsuna's own uncertainties.
- Scratching (引っ掻き, Hikkaki?)
- Biting (噛み付き, Kamitsuki?)
- Lacerating (噛みちぎり, Kamichigiri?)
- Purring (ゴロゴロ, Goro-goro?)
- Ruggito di Cieli
- Mantello di Vongola Primo
- Mitena di Vongola Primo
- Its Japanese name ナッツ, Nattsu? is the inverse of Tsuna's name in katakana, excluding the sokuon "ッ".
- When Reborn wanted a pet for Tsuna, he had suggested a lion.
- Natsu gets along with Enma, letting Enma pet him and play with him. This made him initially hesitate to fight Enma.
- Natsu doesn't get along well with Uri due to his cowardly behaviour and Uri's aggressiveness.