It’s a special Paramecia fruit called the Supa Supa no Mi, Model: Shusui that imitates a Zoan like how the Mochi Mochi no Mi imitates a logia. In reality it’s like the Gomu Gomu no Mi in the fact that it was reclassified as a Special Paramecia from Mythical Zoan. It’s true name is the Hito Hito no Mi, Model: Runo (taken from Lunar, in case you were wondering)