The Neko Neko no Mi, Model: Saber Tiger is an Ancient Zoan-type Devil Fruit that allows the user to transform into a hybrid and full version of a saber-toothed tiger at will. It was eaten by Who's-Who.
Sāberutaigā (サーベルタイガー,Sāberutaigā?) is a Japanese way of referring to the saber-toothed tiger, loaned from the English "Saber Tiger" (though the latter is not used in English).
Strengths and Weaknesses
A user of this fruit's power can transform into a smilodon, a.k.a. a saber-toothed tiger—a powerful, carnivorous predator from the prehistoric era—as well as assume a human-smilodon hybrid form. The ability's current user Who's-Who, who is an already large man, grows to very notable size in his full Beast Form, dwarfing his human-sized subordinates and even the large fish-man Jinbe.
No weaknesses of the fruit's power are known beside the standard Devil Fruit weaknesses.
Who's-Who was shown in his full Beast Form relaxing at the "Nekoka-fé" in Kaido's fortress.
Despite its popular name, the saber-toothed tiger (correctly named Smilodon, which is one of the best-known genera of saber-toothed cats) is not closely related to the modern tiger or any extant feline.
It is theorized that the Smilodon actually possessed a short, stubby tail, unlike modern large cats and Who's-Who's transformation, which bear long tails.
Smilodon have been reconstructed with both plain-colored coats (like Who's-Who's) as well as with spotted patterns (seemingly the ancestral condition for feliforms), both of which are considered plausible.
Befitting his Devil Fruit ability, Who's-Who's closest subordinates appear to follow a cat theme, including several feline SMILE users.