Nooroo is a kwami that is connected to the Moth/Butterfly Miraculous, and with his power, his wearer can use the brooch to transform into a moth-themed superhero, the current wearer being Gabriel Agreste, who uses it as a villain.
Before Season 1
When the idea of transmission came into existence, Nooroo came into existence. Before the Miraculouses were created, Nooroo and the other kwamis traveled all over the universe, unable to interact with humans. Until, thousands of years later, a mage created the Miraculouses.
For the next 5000 years, Nooroo had been dormant in the Butterfly Miraculous, stored in the Miracle Box at the temple of the Order of the Guardians. Helping people all over the world with his powers starting in China. Then, spent time with an unknown female holder.
However, 172 years ago, Master Fu's mistake resulted in not only the destruction of the temple, but also in loss of the Butterfly Miraculous and the Peacock Miraculous. At some point in recent times, Nathalie found Nooroo and the Butterfly Miraculous giving them to Gabriel, and he took them with him back to Paris.
In "Ladybug & Cat Noir (Origins - Part 1)", Nooroo told Gabriel about the Miraculouses and the absolute power one can achieve when wielding the Ladybug Miraculous and Cat Miraculous at the same time. Then, after Gabriel asked him, he explained how the Butterfly Miraculous worked. When Gabriel proclaimed that he would use its power to create supervillains instead of superheroes, Nooroo tried to tell him that the Miraculous wasn't meant to be used for evil purposes, but Gabriel refused to listen and told Nooroo that he was his master and that he must obey him. Nooroo sadly obliged and entered the moth brooch.
Since then, Nooroo's powers were used against his will for evil.
In "The Collector", after Hawk Moth made an akuma, he detransforms revealing his secret identity. When Nooroo asked his master why the akuma was still in his lair, Gabriel explains he has to throw Ladybug and his son off his trail. To Nooroo's surprise, Gabriel denounced him and Nooroo returned to the Butterfly Miraculous. Later, Gabriel released him after his plan worked and he transforms again into Hawk Moth.
While Gabriel entered his lair in "Gorizilla", Nooroo questioned in curiosity if his master believed that Adrien was Cat Noir. After Gabriel explained his suspicion and plan, he transformed into Hawk Moth.
In "Syren", after having witnessed Syren's defeat because of Ladybug and Cat Noir's new powers, Gabriel demanded that Nooroo tell him how he can acquire new powers for himself. But Nooroo said that kwamis don't know the recipes, which Gabriel deduced as being inside the spellbook. Gabriel asked if he could read the spellbook's code, but he insists that only a Guardian knows how, leading to Gabriel declaring that he needs to find the Guardian.
In "Sandboy", Nooroo tried to sneak away from Gabriel but due to his wielder's commands he couldn't. He tried to explain that he wanted to go out for his birthday but was refused to do so. But when Gabriel sensed someone's negative emotions they both went to the lair and transformed into Hawk Moth. In the midst of Sandboy's rampage they both felt the other kwamis connection but after failing to track them down and Sandboy's defeat. Nooroo was questioned by Gabriel if he liked his gift but his concern was turned into fear when Gabriel wanted to capture all of the kwamis.
In "Style Queen", Nooroo saw Gabriel talking to his wife Emilie about his next akumatized villain being his master piece and they transform into Hawk Moth once again.
In "Queen Wasp", when Style Queen failed Nooroo heard Gabriel renounce him and he went into the Butterfly Miraculous. But he was released again by his master when he heard that Gabriel had the chance to akumatized someone with another Miraculous he was shocked and transformed into Hawk Moth. Later, after Queen Wasp's defeat, Nooroo heard Gabriel while talking with his wife.
In "Catalyst (Heroes' Day - Part 1)", Nooroo helped Gabriel transformed into Hawk Moth to initiate his ultimate plan. By using Volpina to doubt Ladybug and akumatizing Natahlie into Catalyst to amplify his powers they both transformed into Scarlet Moth. After the army was assembled at the Eiffel Tower, Scarlet Moth made an appearance and through the news feed the mastermind demanded that the heroes surrendered. Before challenging the heroes to an all out war.
In "Mayura (Heroes' Day - Part 2)", during the battle against the French Miraculous superhero team, despite turning their allies against Ladybug and Cat Noir. Scarlet Moth was surprised to see all of Paris rise up against them, despite the mastermind's attempt to akumatize the heroes the cane was destroyed and they destransformed back into Hawk Moth losing the akumatized army. However the villain was able to defeat the duo in combat before finishing them off they were halted by Rena Rouge, Queen Bee, and Carapace. Backed into a corner the mastermind received help from Mayura and escaped, and the base of the tower they detransformed. Nooroo expressed worry about Gabriel after he was defeated and returned to the mansion.
In "Backwarder", Nooroo was leaving with Gabriel and his son to attend a wedding in London. That was until Gabriel sensed Ms. Lenoir's negative emotions after thinking of an excuse to delay the train they transformed into Hawk Moth and akumatized her into Backwarder.
In "Party Crasher", Nooroo along with Gabriel went down into their secret room where they gathered some more white butterflies. However, just as they were about leave, Adrien's increasing secret caused a power outage with that they transformed.
In "Stormy Weather 2", when Gabriel sensed a familiar negative emotion Nooroo suggested they might by Adrien's trying to convinced Gabriel to spend more time with him. But Gabriel retorted saying that he was doing this so Adrien could be happy again and yet Nooroo warned him of the dangers of losing his son if he continued this dark path and once again tried to convince Gabriel to his powers for good. But he was silenced by his master and transformed.
In "Timetagger", after Mr. Pigeon was defeated once again Hawk Moth attempted to destransform but soon sensed the presence of another villain from the future named Timetagger. When the mastermind believed that the Miraculous were finally achieved, they were informed that the Hawk Moth that akumatized him wasn't Gabriel. Once Timetagger was defeated, Nooroo and his master detransformed, he tried to say something but was silenced by Gabriel leaving their lair.
In "Reflekdoll", after Reflekta and her sentimonster's defeat, Nooroo and Gabriel detransformed and after Nathalie and Duusu did so too. He was taken aback by his friend's enthusiasm worried about his mental state.
In "Ladybug", soon they transformed into Hawk Moth once again and by akumatizing Nathalie into Catalyst once more they powered up to Scarlet Moth again. This time sending a swarm of scarlet akumas to the school, in an attempted to akumatize everyone but when Nathalie's condition got worse the plan was called off and they detransformed. Soon after a while Gabriel woke up and saw Nathalie transformed Nooroo was asked why he wasn't woken up. Nooroo said he couldn't since he was sleeping peacefully and they retransformed to save Mayura. Once back at the mansion Nooroo heard Gabriel say that Nathalie's time as Mayura was over.