Sento Sento no Mi

Introduction
The Sento Sento no Mi is a paramecia devil's fruit that allows the user to gain strength by shouting battle cries and swinging their weapon(s). There is no current user, and the devil's fruit is located in the Devil's Fruit Vault.

Strengths
The user is able to infinitely scream and swing their weapon, and in turn, gain infinite power. It is very useful in the sense that a single punch can break mountains if the user swings their weapon/shouts a battle cry.

Weaknesses
Accumulating incredible power take a lot of time. To have enough strength to split a rock, the user must do the aforementioned action for at least six minutes. The user also has this insane strength bonus for only one hit. From then, the user must charge all over again.