Seiu Seiu no Mi

The Seiu Seiu no Mi is a Logia-type Devil Fruit that allows the user to create, control, and transform into Nebula at will. "Seiuseiu" is the onomatopoeia for the sound that billowing Nebula makes. Seiu is from "Seiun", which is Japanese for "Nebula". In the Viz English manga and FUNimation dub, this fruit is called the Nebula-Nebula Fruit, while in the 4Kids dub, it's called the Cluster-Cluster Fruit. It was eaten by Junsui Kamui.

Strengths and Weaknesses
The user of this fruit is able to generate, manipulate, and become any type of Nebula. Like most other Logia Fruits, when Kamui is hit, he can simply use the fruit's power to become Nebula, thus absorbing the attack and remaining unharmed. Like some of the other Logia type Devil Fruits, this one allows his user to "fly", by turning his body or the lower part of it into Nebula, greatly enhancing his movement speed.

The main offensive capabilities of the fruit stem from his user's ability to change the density of the Nebula produced at will. This allows Kamui to surround his targets with his interstellar cloud of dust and then, solidifying it, to grasp them.

The Nebula can also be used as a blunt weapon, hitting enemies with great strength. However, it is possible to escape the smoke's hold with a sudden, strong enough expansion of the body (such as Apyros Devil Transformation). Thanks to this fruit he is almost invincible against most enemies.

It would seem that when confronted by fire or Smoke, they will cancel out one another. With his current mastery over his powers, the only reliable way to injure Kamui is through the use of Haki, as Momonga did during their short battle, or through the standard Devil Fruit weaknesses.

Usage
Kamui has mainly used the Nebula Clouds produced by his fruit to capture his opponents. He can manipulate the Nebula's density to make it thick or thin, allowing him to hold and constrict others within it. Like most Logia users, he can fly by turning his lower body into smoke and propelling himself like a rocket.

He covers his targets with an intangible Nebula Cloud, then solidifies it to make the capture or a strike.

Trivia

 * While most Logia have been shown to have some natural enemy or are inferior to another Logia, it is still unknown what "Nebula" is weak against. However it has been shown to be ineffective against some Devil Fruits; Ace's fire and Smoker's smoke had no effect on it.