Gomu Gomu no Ono, also known as Gomu Gomu no Axe or Rubber Rubber War Axe in English renditions, is currently now taking a technique done exclusively by Monkey D. Luffy in the series One Piece. It is written in Japanese as ゴムゴムの戦斧, with the word "ono" translating literally from the term into "war axe". This is one of Luffy's earlier attacks and he has been throwing it since then.
To execute the Gomu Gomu no Ono, Luffy stretches one leg as high into the sky as possible and brings it down with immeasurable force towards his enemy. It has the movement of swinging an axe, hence the name of the move. This attack is recognized for its might, especially effective against structures or large enemies.
One of the most memorable uses of Gomu Gomu no Ono was during the Arlong Park arc when Luffy used it to batter down and destroyed Arlong Park itself. This moment turned out to be important not only in terms of strength for Luffy himself but also as a very symbolic act for Nami's village to release themselves from Arlong's tyranny.
As Luffy's powers developed throughout the series, so did the uses of Gomu Gomu no Ono. Upon the development of Gear Third, Luffy was able to inflate his bone structure with air, which makes the size and power of his attacks drastically larger. This allowed a Gear Third version of Gomu Gomu no Ono with increased power of destruction.
Being one of such early prominent techniques, some fans of One Piece have mentioned that Gomu Gomu no Ono has been less used recently within the later arcs. This is a change in combat style by Luffy himself, yet with his individual evolution as a combatant and the more sophisticated techniques introduced, there is less of a requirement for him to make use of his sinful body. Of course, the core concepts at the attack—using Luffy's stretchiness for impactful, vertical strikes—stay with many of his later techniques.
Precisely like the majority of Luffy's techniques, what really puts Gomu Gomu no Ono at the top is not so much its sheer power but the way he tails the power of his Devil Fruit. Once considered not the most fearsome of all Devil Fruits in the One Piece world, the Gomu Gomu no Mi changed with ingenuity that Luffy displayed. The creativity during the bout is another classic example of what One Piece is all about. It cements the notion that a Devil Fruit user is never truly about the powers at their disposal but about the imagination and the will to succeed.
Whenever doing these combat evolutions for Luffy, many fans speculate about the many improvements that could have been made to his classic moves. For instance, people have suggested that Gear Second, or Gear Third Gomu Gomu no Ono, enhanced with Haki, could be a super powerful finisher move; it isn't, and, of course, it never is presented as such in the series.
Techniques like Gomu Gomu no Ono can be used as yardsticks to relate Luffy's power at the moment to his previous encounters with villains. For instance, with the not-so-distant past, he may have had to use attacks like Gomu Gomu no Ono against an enemy like Axe Hand Morgan, who would probably have seen him early in his adventure as a fruit of very low-hanging opportunity. Well, Luffy's repertoire nowadays includes much more potent attacks, like Gear Fourth Boundman, and applications of advanced Haki.