Kwamis are sprite-like, "abstract" creatures that give certain power to people with Miraculouses, transforming them into animal-themed super beings.
As explained by Wang Fu, Wayzz, and Tikki in the second issue of Miraculous Adventures, kwamis are formed whenever a new abstract idea or emotion comes into existence in the universe, such as creation, love, beauty, and mathematics. These emotions can came into being at different times, such as the kwami of creation, Tikki, who was formed at the beginning of the universe and thus was the first kwami to exist.
All kwamis know each other and were able to journey across the universe for a very long time. However, the kwamis couldn't be sensed by regular tangible creatures like humans and thus were unable to interact with them. The issue was solved thousands of years ago, when a Chinese mage figured out how to create magical jewels, Miraculouses, in order for the kwamis to be able to communicate with people.
From that point on, kwamis helped the wearers of their Miraculouses achieve good around all the world, although there were instances where they became stuck with villainous holders and forced to help them with their diabolical schemes due to being bound to their holder's every command.
A long time ago (even enough for some kwamis to forget), they were blocked by a magical spell that prevents them from speaking the name of their owners so they wouldn't be allowed to say their holder's real name to other kwamis.
All kwamis know the Guardian of the Miraculous but aren't allowed to reveal him to their wielders unless of great emergency, like in "Princess Fragrance", "The Collector", and "Syren". Kwamis all feel a sense of familiarity with the Miraculous spellbook when they see it, implying certain past with it.
Even though kwamis are familiar with the book, they don't know how to read it, as revealed by Nooroo in "Syren". This is because kwamis must never know the spells that are inside the book, which is meant as a precaution should a kwami fall into the wrong hands.
In "Sandboy", active kwamis collect items from the outside world inside the Miracle Box so kwamis bring presents to inactive ones for entertainment.
Also, according to Tikki, kwamis aren't allowed to leave their Miraculous wielder's side in case someone becomes akumatized.
Generally, kwamis are small, being around 10 centimeters in height, with large heads and tiny bodies. They have arms and legs, but they lack fingers and toes yet are still able to lift things. The animal theme that they display is reflected in their Miraculous, Plagg is black with green eyes, cat-like ears, and a cat-like tail thus fittingly his Miraculous is the Cat Miraculous.
When drinking certain potions made from the Miraculous spellbook their appearances will change. If the aqua mode potion is used, the kwami will gain fins and a tail. When it comes to "ice mode", the kwamis gain crystals on their bodies.
Kwamis can become intangible to pass through solid objects, like locker doors or chains. In "The Collector", it is noted that they aren't able to be filmed or photographed, not showing up in photos and videos to prevent others from discovering their existence. Normally, kwamis can fly and levitate, even at high speeds as shown by Plagg .
Even though they are small, kwamis appear to have enough strength to hold things that are larger and/or heavier than themselves.
Kwamis inhabit pieces of Miraculous jewelry in order to give the person wearing them the ability to transform into superheroes and gain a specific power based of the abstract idea or emotion that made the kwami come into existence, such as Trixx granting the power of illusion via Mirage. They are aware of the actions of the people who possess their Miraculous when transformed, but they cannot communicate with their holders when they are transformed. For example, Plagg laughs at how Adrien said rude things to Ladybug when he was possessed by Dark Cupid's arrow. At the same time, the extent they can be aware what is happening when their Miraculous is used is uncertain in "Ladybug & Cat Noir", Tikki and Plagg appear to be unaware whether the akuma was captured or not.
The Miraculous transformation can last indefinitely unless the Miraculous' special power is used, at which point the wearer has about five minutes until they revert to their normal form and the kwami leaves the Miraculous. To regain power, to strengthen themselves, and to transform their wearer again, they need to refuel by eating food. Some ones have a preference for specific foods: for instance, Plagg's favorite food is Camembert cheese, but he is willing to eat other types of food if Camembert isn't available for him. Despite their ages and powers, kwamis can get sick, as seen when Tikki becomes sick after helping Marinette defeat a villain in pouring rain. Wang Fu is able to assist in their recovery and heal them. Despite the fact that they can become ill, it is unknown if it can only occur while bound to a Miraculous, or to which extent this could harm them. As abstract entities, they have been around since before the creation of the Miraculouses, meaning, even if their Miraculous is destroyed (by Cataclysm) or being erased from the timeline, they return to their natural state, in which they cannot be perceived by human senses under normal circumstances; they do not cease to exist. It is also not known if they are truly immortal. Based on their origins, they may live on forever after coming into existence. Also, the ideas, concepts, or emotions that create them are seemingly not bound to other beings, since Tikki was born alongside the universe, and not due to the concept of creation being discovered or realized at a later point in time.
Kwamis also perform a ritual for their Miraculous holders where they create a kwagatama inside their bodies from the hairs of their past and current holders. They then present the charm to their current bearer for a special occasion, such as a birthday.
Kwamis can communicate with each other once in every “cycle” on their birthday, if they gather in the Miracle Box at a specific time and sing all together. The more kwamis there are the stronger the connection. They also can dispel the connection with their hands. If a kwamis powers are active during that time frame, the other kwamis will contact the Miraculous' holder and the Miraculous holder can track them down if they stay connected, apparently being the only way a kwami's wielder can communicate with them when they're in their world.
Kwamis are able to perform their respective Miraculous holder's power without their jewels, but a much greater extent which can even turn uncontrollable. This is shown when Plagg was able to perform Cat Noir's Cataclysm by coming into direct contact with the Eiffel Tower's floor and thus destroying the entire structure in "Style Queen".
As of recent Season 3 spoilers, since the Miraculouses have the power to fuse together making a hybrid form of wielder's suit, it's implied that kwamis are capable of fusing their powers together even though isn't fully known how it's done.
Potions from the Miraculous spellbook are able to alter a kwamis appearance and form by drinking the potion directly or consuming something that contains it. Besides modifying a kwami's appearance and form, potions also help the wielder get new abilities and appearances in their superhero form, depending on the potion the kwami consumed.
The known power ups are:
Water - The kwami's legs are replaced with a fish tail, their hands are replaced with flippers, and change their appearance with additional flippers on their feet. It allows the kwami to grant underwater abilities to their holder. The potion's color is green.
Kwamis seen with the underwater power up: Aqua Tikki, Aqua Plagg
Ice - The kwami grows three ice shards somewhere on its body, while in some cases some parts of their bodies, such as Tikki's circular spot, turns into a hexagon. It allows the kwami to grant ice-related power to their holder. The potion's color is light blue.
Kwamis seen with the ice power up: Stalac Tikki, Plagg Glacier
Inhabits the wearer's jewelry for them to change into a dog-themed hero.
The concept of the kwamis was created by Bandai.
According to Thomas Astruc during a Miraculous panel at Ludicomix 2018, the kwamis are inspired by the Chinese zodiac signs because he wants the world to get to know the elements of the oriental culture.
A teaser trailer released on August 31, 2017, revealed that some of these new kwamis are based on the animals of the Chinese Zodiac.
A kwami is a "quantic (small) kami." In Japanese, kami (神) often refears to god or certain kind of spirits.
Wilfried Pain noted in a Twitter response that kwamis are "some kind of god" and don't exactly have genders. He also mentioned that the kwamis are supposed to look very cute.
Nonetheless, in “Sandboy”, kwamis refer one another (Sass as an example) as brothers or sisters.
According to Thomas Astruc, the name of every kwami has to be a short name with a double letter in it. However, Nooroo's name has two doubles, whereas the others have just one double.
Kwamis are like Aladdin's genie, having to obey their holders' desires. They aren't genies, however, they exist in-universe, according to Plagg in "Ladybug & Cat Noir".
It is unknown if kwamis can be akumatized, but Season 2 will have the answers, as revealed at the Miraculous Ladybug panel at SDCC 2016.
In "Queen Wasp", kwamis can be akumatized indirectly (except Nooroo himself) if the Miraculous they're inside of becomes the akumatized object.
If the Miraculous jewel gets destroyed, the kwami reverts to their spirit form, unable to be seen by living beings anymore.
According to Jeremy Zag, Season 2 will include an episode revealing the origins of the kwamis.
The New York Comic Con 2016 panel additionally noted that there would be Miraculous Secrets webisodes that focus on the kwamis, notably Tikki and Plagg (revealed as "Tikki" and "Plagg"), and that there may be more than one episode in new seasons that centers on them. Which is revealed to be "Sandboy".
The official Miraculous Ladybug Twitter account noted that while more kwamis will be seen in Season 2, it won't be all of them.
According to Tikki, in "Sandboy" a kwami's cycle or birthday is equivalent to several hundreds of human years.
↑In Style Queen (Queen's Battle - Part 1) Plagg comments on going "too far" with dinosaurs when he was young, in real life they are estimated to have gone extinct approximately 65 million years ago, though this is not a number which has been mentioned in the show.