noun
one's nature; inherent character; destiny
Refers to a person's innate disposition, temperament, or the fate that seems to come from that nature. Often used in expressions like 性だから (it's just my nature) or 性には逆らえない (you can't fight your nature).
怠け癖が直らないのは、もう性だから仕方ない。
I can't fix my laziness; it's just my nature, so there's no help for it.
彼の性には逆らえなかった。
He couldn't go against his own nature.
noun
custom; tradition; habit; convention
Used for long-standing customs, traditions, or deeply ingrained habits of a group or society. Often carries a nuance of something that has become second nature through repetition.
この村では、祭りの準備はみんなでやるのが性になっている。
In this village, it's a custom for everyone to prepare for the festival together.
長年の性で、朝
Out of long habit, I always read the newspaper in the morning.
性質 is a more general and objective term for properties or characteristics of things or people, while 性 (さが) emphasizes innate, often unchangeable, personal nature or destiny.
習慣 is a neutral word for a habit or custom, while 性 (さが) in the sense of 'habit' implies a deeply ingrained, almost instinctive custom or tradition.
The reading さが is native Japanese, and the kanji 性 is conventionally associated with the meaning of 'nature' or 'disposition'. The exact historical derivation is uncertain.