Jonetsu Clan

The Jonetsu Clan are a branch clan that are descended from the Uchiha Clan, they can trace their history all the way back to the founder - Jonetsu Uchiha who left the clan and started her own.

Demise
Meoru Jonetsu was due to be the next head of the Jonetsu Clan, as she was part of the main founding family. However the Yuki Clan (the sworn rival of the Jonetsu Clan) decided to kill her, luckily a fellow ninja slew the assassin that came after her but it had a huge knock on effect. The Yuki Clan demanded compensation for the death of their comrade and the Jonetsu Clan agreed to fulfil one wish, the Yuki Clan told them to not fight for a day and in that day they where attacked and utterly destroyed.

Kekkei Genkai
Their kekkei genaki seems to be the Blaze Release, it is currenly unknows how the can manifest the black unhallowed flames despite no having the Mangekyō Sharingan dojutsu.