Serenity is purely fictional. The story and characters were made up by the creators for entertainment purposes. There's no connection to any actual events or individuals in reality.
In Naruto fanfic, 'Hassan of Serenity' could be an original character created by the fanfic writer. Usually, such a character is designed to fit into the Naruto universe's existing themes and power systems. It might be a character with special abilities related to serenity, perhaps having some form of unique jutsu or a calm and collected personality that stands out in the often chaotic world of Naruto.
As a fan of web novels, I don't have any knowledge about palace politics. Palace strife was a literary theme in ancient China, usually referring to the struggles and conspiracies in the palace. It involved politics, power, love, desire, and many other aspects. It was highly artistic and dramatic. If you want to know more about palace fights, I suggest you read related literature or search for online resources.
Isolation is a common theme. In 'dark serenity fanfiction', characters might be isolated either physically, like being alone on a desolate planet, or emotionally, such as being shunned by their own kind due to some dark secret.
In the Naruto fanfic, Hassan of Serenity could possess a range of abilities. Maybe they have a special kekkei genkai that is related to the concept of serenity. For example, they could be able to create illusions of peaceful landscapes that disorient opponents. Or they might have the power to absorb negative emotions and convert them into positive energy that they can use for various purposes, like strengthening their own attacks or healing. Their serenity could also give them an edge in stealth, as they can move quietly and calmly without arousing suspicion.