Hand signs are considered to be an integral part of the Naruto series as this famed aspect almost goes synonymous with the series’ name. Being the gateways to kneading chakra and casting ninjutsu, hand signs naturally hold a valued position in the shinobi world. A shinobi’s skill is evident from how fast these hand signs are performed, with the number of hand signs required also determining the level of mastery. Similarly, another concept attributed to superior skills is the one-handed hand sign, though this concept has been rarely seen in the series.
One-handed hand signs were initially revealed in the first major arc of the Naruto series, however, the concept was given the backseat as these distinct hand seals soon disappeared, only to make an appearance once more in the final arc. It's rather odd for such a unique concept to fade into the background despite having such significance attributed to it, though several reasons do justify why incorporating such hand seals would have been incongruous for the story.
Instances of One-Handed Hand Signs
Given the exclusivity that surrounds single-handed hand signs, it's only natural for these hand seals to be used in only a handful of instances. However, it’s the peculiarity of the very same instances that make the use of these hand signs highly inconsistent. The very first use of one-handed hand signs was during the Land of Waves arc, with Haku revealing his distinct style of hand seals while fighting Naruto and the rest of Team 7. Kakashi even states that he had never seen anything like that before, a statement that says a lot considering Kakashi has copied over a thousand jutsu and has seen an immense number of different hand seals throughout his lifetime.
Even if it were the first time Kakashi had witnessed such a unique style of casting jutsu, it's rather odd that there was no mention of this anomaly after that arc, only to be used once more during the Fourth Great Ninja War. In fact, the only reason these hand signs were witnessed once more was due to Minato’s arm being severed off, leaving him no choice but to use single-handed hand seals to save Naruto’s life. This indicates that these hand signs made an appearance simply to serve as a plot device and nothing more.
These hand seals were shown once more in the Boruto series with Sasuke being forced to utilize them due to his missing arm, a similar case to Minato. However, such usage is highly inconsistent from the story’s perspective given the concept of these hand signs is supposed to be unknown to most shinobi. Even if Sasuke and Minato had knowledge of such a way of casting jutsu, they were never witnessed using these hand signs before, clearly indicating their usage out of pure necessity and way to keep the plot moving. A few plausible reasons do justify why these were the only instances of using one-handed hand signs, explaining why it was necessary to relegate this concept to a mere one-time phenomenon.
One-Handed Hand Signs Are Inefficient
The speed of casting hand signs is indicative of a shinobi’s skills as this not only allows the jutsu to be cast much faster but also bars the opponent from discerning which jutsu is being used based on the subsequent hand signs. However, one-handed hand signs are extremely slow compared to their regular counterparts, giving the opponent enough time to either counter the jutsu or stop the caster from using the technique altogether.
One-handed hand signs are more useful in situations where there’s no other choice but to use one hand, especially since every single instance has involved one hand either missing or already in use. This deems these hand signs as nothing more than a last resort to casting jutsu in a dire situation and not something regular shinobi could employ in everyday situations. These hand seals could have been useful for regular use, but the incredibly low speed makes one-handed hand signs highly inefficient.
Hand Signs as a Whole Became Less Common
After the initial parts of the series, the concept of hand signs as a whole became less apparent. Jutsu that didn’t require hand signs took the center stage and those that still did no longer required the same amount of hand signs. These were all efforts to reduce the amount of times hand signs had to be drawn since constantly creating hand signs was extremely redundant and time consuming for the author.
With Kishimoto already trying to curb the amount of hand signs in the series, it wouldn’t make sense to incorporate one-handed hand signs permanently since it would require the seals to be drawn in every instance. Given the redundancy that came with drawing regular hand signs, incorporating a new concept based entirely on hand signs would have simply made it difficult for the artists to draw, resulting in the author forgoing the concept entirely.