It allows to absorb natural energy from the environment easily, without any risk, which increases the power of ninjutsu and taijutsu.
The Senji story
Senjitsu Senji, from the Land Of Hot Water, who was a scientist, married Hadime, that possesed this kekkei genkai, this woman is Mirane's mother, who died in Senjitsu's hands while experimenting with her dōjutsu when their daughter was 4 years old.
For Mirane not to ask why she doesn't have a mother, Senjitsu married her twin, which name's unknown, thus Mirane won't realise her mother died. This twin also got pregnant, and Mirane's sister was born, however, unluckily, the twin died in the act. To honor her twin, he called his baby Hadime. This all happened when Mirane was 6 years old, and because these tradegies, Senjitsu started to experiment with her. He did it for 2 years, and after raping Mirane, he decided to try his experiments with Hadime, but the daimyō discovered what Senjitsu was doing and he went exiled from the Land Of The Hot Water.
It is unknow what he was doing exactly with them, but he returned, 5 years later, to the Land of Hot Water for Mirane and kidnapped her. He was being awfully chased til the Land Of Fire, near Konohagakure, where he left Mirane with amnesia after telling her that she was a dishonour. Strangely, was the Raikage who saw her and saved her, thus she became a Kumogakure genin.
When Hadime was 16, he came back to the Land of Hot Water for her, kidnapping his daughter again, running through the Land of Fire again, but this time they captured and locked him in prison. Unhopefully, he left Hadime with amnesia. When she woke up, not remembering who she was and where she came from, went to Konoha, that was near, to investigate why she was there.
One year passed for Hadime to know her past.
The Kazekage gived Sherlynn and her squadron (with her boyfriend, Takeshi; and her fraternal twin, Daichi) a S Rank mission, in which they had to rescue the elderman Matsuboshi from a big terrorist group. Before getting to the point the enemy group was, they got concealed by a large amount of ninjas with Mirror Release kekkei genkai, who transformed in each one of the squadron. They couldn't recognise who was the real other, so they just kept their backs close to not harm the real ones, but the battle turned to a havoc.
Unluckily, the enemy reached their objective: to kill Sherlynn by Senjitsu's commands, because she possesed the Kyoudogan too.
Senjitsu is free and still alive, no one knows how. However, he is looking for Hadime and Mirane sending manipulated groups of people with several kekkei genkais (or implanted by Senjitsu just for the chase).
- Although Daichi and Sherlynn were fraternal twins, Daichi didn't had the Kyoudogan naturally.
- Daichi got his right eye harmed during the battle, so they took one eye from his sister for him to see. After his sister's death, he changed his ways and look radically, so that no one recognise him never.
- It's unknow where is it from.
- Hadime awakened her dōjutsu at 16, while Mirane did it at 5.
- Both Mirane and Hadime discovered that they had this genjutsu at 22 and 16 respectively.
- People with Kyoudogan are born with pink eyes, and a darker pink ring appears in the middle when it's awakened. Also it appears while absorbing natural energy.