Shinobi (忍 Stealth), otherwise more commonly referred to as ninja (忍者 Stealth Person) are individuals who are capable of employing chakra (チャクラ, Chakura) in order to form Jutsu (術 Techniques), which are supernatural abilities that revolve around specific usages of chakra in order to form a wide variety of effects, and are normally used in tandem with hand seals.
Shinobi aren't of any unique race, and are simply humans who are capable of utilizing supernatural abilities through the employment of chakra. They are normally very physically inclined, and are capable of physical feats beyond the average human thanks to their standard training regimes.
Shinobi are generally very loyal to their own countries, and will conduct missions of any kind, ranging from mundane missions to life-threatening ones. Any Shinobi who defect from their village are labelled with the title, Missing-nin (抜け忍 Runaway Shinobi).
Shinobi are generally very humane in appearance, considering that they are humans after all. However; if one conducts experimentation upon themselves, or has unique DNA that allows for mutation in their body, then they can appear significantly different from what one would expect of a human. As for attire, generally Shinobi wear the apparel of their countries, or specific attires suited to their own needs.
The most defining ability of any Shinobi is the ability to manipulate chakra in order to utilize these mystical arts. Jutsu come under a very wide classifications, with the main three branches being Ninjutsu (忍術 Ninja Techniques), Genjutsu (幻術 Illusionary Techniques) and Taijutsu (体術 Body Techniques). Many commonplace Jutsu allow the user to make clones of themselves, substitute their body with another item, or create an elemental effect with one of the common elements which Chakra is converted to, these being: Lightning, Fire, Wind, Earth and Water. Furthermore; Jutsu could also entail the use of one's own body as a weapon, or by disrupting the chakra flow in one's brain to form illusions.
Tools are also very prominent within most Shinobi. If one is unable to utilize their Jutsu, or simply doesn't want to expend senseless chakra, they can resort to the use of tools as a substitution. Many tools fill a wide variety of purposes, but most include weapons and/or supplementary items such as medicines and self-enhancing drugs. Furthermore; each Shinobi when accepted as a full-fledged Shinobi must wear a headband signifying their loyalty to their country, and few Shinobi Clans are capable of utilizing animals as "tools" in battle, to support them.
Genin (下忍 Junior Ninja) are the lowest rank of ninja, and have recently been promoted from an institution which cultivates Shinobi, which is commonly called an academy. Genin are generally sent on lower ranked missions to do mundane tasks, and get paid for them proportionally. They are also put in four-cell teams, with a single, higher-ranking sensei, who guide them as they promote themselves to Chūnin, and later, Jōnin. In terms of ability, Genin are generally not very strong, unless they're a particular natural talent or possess a vast amount of chakra. Otherwise; they are normally average in most skill-sets, and use their time as a Genin to refine these skills.
Chūnin (中忍 Journeyman Ninja) are the second rank of ninja, and are capable of leading other ninja on expeditions and act as teachers in the respective Shinobi academies. They are commonly sent out on C-Rank to B-Rank missions, and can vary in terms of skill and experience.
Jōnin (上忍 Elite Ninja) are the highest rank of ninja achievable aside from that of a Kage. They are often sent on A-Rank Missions as a result of their skills, and experienced ones are sent on S-Class missions. Jōnin often go on missions alone, unless the mission is particularly dangerous, and are highly skilled ninja with a wide amount of experience in all ninja skill-sets. Jōnin are generally assigned three-man cells of Genin to supervise over their initial tenure as Genin, helping them to grow and become beneficial assets to the village as they do so.
- Tokubetsu Jōnin (特別上忍 Special Elite Ninja) are those ninja who possess Jōnin-level skill in a particular aspect of Shinobi skills and are thus promoted to perform specific duties within their own village or country. An example of this is a ninja who has Jōnin-level skill in Genjutsu, but has Chūnin-level skill in other areas.