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The Modern Guide to the Ancient Text: Book of Ninja (Part 1: In-jutsu)

The Modern Guide to the Ancient Text Book of Ninja (Part 1 In-jutsu)

Ninjutsu: What Is It?

The art of the ninja comprises of two equally balanced skills. In-jutsu and Yo-jutsu make up this ancient art.

Nin-jutsu is the art of silent movement and successfully infiltrating the enemy to accomplish a goal. Yo-jutsu is the skill of hiding in plain sight whereas In-jutsu is the art of “stealing in” or infiltration without being seen.

According to the Bansenshukai (the Book of Ninja): “Though in-nin is not as good as yo-nin, if you have only yo-jutsu but no in-jutsu you cannot gain any benefit from it.” These two are meant to be used in balance.


The Japanese term “Jutsu” means a technique, method, spell, skill or trick. There are many Jutsus, for example: Bajutsu is the skill of riding horses.

In-jutsu can be used to infiltrate a house or a castle. There are specific instructions on how to approach each place a ninja plans to infiltrate. The Bansenshukai gives pointers on how to infiltrate while the enemy is off guard and/ or negligent.

Brain Before Brawn

The art of In-jutsu requires one to plan out the attack before beginning a mission. A good Ninja studies out the best places and times to infiltrate. There are tons of ways a shinobi can infiltrate his enemy including working with someone inside the castle and entering in a secret compartment of a delivered crate, infiltrating on the night of a wedding, during an illness, or after a funeral, using your allies’ raid as cover and so much more!


To infiltrate the enemy at night, it’s important to know their sleep schedule. There are many ways of estimating a sleep schedule based on weight, age and season of the year. The Ninja also need to study how to tell if people are asleep or not.

The Book of Ninja also contains information about how to walk silently, pick locks and hide successfully for long periods of time.

A Plan of Escape

It also comes up with some genius techniques of how to escape if your enemy awakens, including simply staying still and turned away from him, raising the alarm and pretending to be a pursuer of the attacker instead of running, going to the front gate and stating that it needs to be opened because the lord must leave immediately and many more smart and amusing plans.


Part of in-jutsu is setting undetectable traps for the enemy. These include alarm clocks of sorts that startle the enemy and wake you up, literally just bending a bamboo stalk back so that it hits your enemy in the face when they open a door, a trap which drops a heavy board on your enemy, and a disguised pit for the enemy to fall into.

Half of an Art

We now have one piece of the Nin-jutsu puzzle. Next, we’ll be talking about the other half: “Yo-jutsu” or the art of hiding in plain sight.

About Kevin Miles

Kevin started Kage Ninja Gear in 2009 and still runs it to this day. When asked about his company, he proudly states: “We do one thing and one thing only at Kage…we make kick-ass Ninja Uniforms!”

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