Hand Seals, aka kuji-in (literally means "nine syllables seal") are ritualistic hand gestures that are commonly used as part of a magic formula, with roots in Taoism. They are similar to Mudras originating from Hinduism, another type of symbolic hand-gestures (but can include other parts of the body). Also ninjas, and others who use them often also Call their Attacks, so they may be considered Mantras as well.
This trope is popular in Japan (and China), as they're the source of the trope. However, you can expect some works from other countries feature this as well, often parodied. One of the ninja cliches (along with smoke bombs, kabuki stagehand costumes, and shurikens), but sometimes monks also do this as well, especially when meditating.
The mostly used hand gesture in works is the index and middle finger of both hands pointed up, while the ring and little finger wrap the other hand, as shown above. Another variant is the clap palms, more commonly used by monks. Sometimes a one-hand variant is also used.
- Commonly used to do jutsus in Naruto, with the hand gestures represent the 12 Eastern Zodiac motifs (the picture above, in particular, represents "sheep/ram"), but other variants also exist, such as Naruto's crossed index and middle fingers when he use the Shadow Clone Jutsu.
- Bleach characters sometimes (but not always) do this when using kido spells. Some examples: Hacchi using Bakudo #99, Rukia using Bakudo #9, Shuhei Hisagi using Bakudo #62.
- Sometimes used in Fullmetal Alchemist with alchemy.
- In Sailor Moon Hino Rei/Sailor Mars uses these combined with a paper charm to perform Akuryo Taisan, which paralyses enemies. She can use it as either Sailor Mars or Rei Hino as it has to to with her being a Miko.
- Averted in Ghost Hunt, where the Nine Syllables are used for exorcism, but not with the appellated seals. (A more generic two-fingered gesture is used instead)
- Ga-Rei: Kagura uses a certain hand gesture to release Byakuei's seal. As shown in Ga-Rei -Zero-, she can release Byakuei without making the seal, but only when she's extremely distressed.
- Marron and Carrot from Sorcerer Hunters explicitly notes that the Eastern-style magic Marron uses requires two hands to perform the necessary seals in order to cast magic, contrast to the Western-style magic utilized by Sorcerers.
- In RDG: Red Data Girl, Miyuki teaches Izumiko the ritual of kuji-kiri, "cutting the nine seals," as a protective charm.
- Of course it reigns supreme in the Power Rangers and Super Sentai series with a ninja theme or ninja-themed bad guys (mainly Ninpuu Sentai Hurricaneger/Power Rangers Ninja Storm). Bonus points for a smaller robot using hand seals to make the bigger robots combine, and a Butt-Monkey comedic villain stealing from a ninja Big Bad by imitating the ninja gesture to make a door open.
- Spoofed in Kamen Rider Fourze at the opening: Fourze turns invisible with the Stealth Switch, but he really didn't need to do a hand seal to do it.
- Hanzo Hattori and Kotaro Fuuma from Samurai Warriors both use this kind of spell, ususally in order to lock/unlock a gate.
- Phantom, the ghost ninja robot from Mega Man Zero uses this to do the Doppelgänger Spin.
- Cubit Foxtar of Zero 3 uses a one-hand variant to summon his 9 Attack Drones.
- Guy, of Final Fight and Street Fighter fame, is sometimes seen performing one-handed seals (like Haku, but he predates him by about a margin of a decade) when performing moves such as his Bushin Senpuukyaku or Bushin Musou Renge. Two of Guy's Victory Poses in Street Fighter Alpha consist of 'em (one them with his back to the player). In Super Street Fighter IV, two of his personal actions, his Focus Attack, and his end of match win pose also involve hand seals, in addition to the above.
- One of Raven's win poses in Tekken is reciting the lot. Humorously, if playing Yoshimitsu's story mode in 5 and lose to him, you can watch Raven try to teach him the kuji-in. Yoshimitsu cannot get them right. Is Yoshimitsu sure what he's practicing is ninjutsu?
- Greninja, the ninja frog Pokémon introduced in X and Y, performs a hand seal whenever it uses a special move.
- Final Fantasy XIV's Ninja job uses hand seals called Mudras to invoke the majority of its abilities. Messing up the order of the signs will summon a rabbit onto your head for the sole purpose of announcing your failure to anyone around you.
- In City of Heroes, the "Ninjitsu" powerset makes notional use of the Rin, Sha, and Retsu gestures for avoiding status effects, self-healing, and temporary extreme performance respectively. However, given that the character models don't have animatable fingers, you can't tell the gestures apart except through their associated visual effects.
- In Dominions, this is the basis for the "* sign" spells, available to the monks of Jomon
- The King of Fighters XIV newcomer Banderias Hattori uses several before executing his Climax Desperation Move.
- Batman: The Animated Series: Kyodai Ken frequently uses this.
- Fridjitzu requires this.
- Teenage Mutant Ninja Turtles (2012): In the Season 3 episode "The Deadly Venom", Master Splinter teaches Leonardo to chant and perform the handseals for a special Healing Hands technique. This power becomes key in the following episodes.