Kaze no Stigma

Four years ago, Kannagi Kazuma was defeated by his cousin Kannagi Ayano for the right to be the successor of Enraiha, a sword passed down in the Kannagi family. His defeat, along with his lack of talent for En-Jutsu (The fire arts, and is also the Kannagi Clan's specialty), resulted in his banishment from the family. Now, Kazuma returns as Yagami Kazuma, a skilled master of Fuu-Jutsu (the wind arts). At the same time, a number of murders at the Kannagi residence perpetrated by a powerful Fuujutsu-shi cast suspicion on him.
Note: The work is unfinished due to the death of the author.
(Source: Wikipedia)