noun, na-adjective
innate cheerfulness; sunny disposition
Describes a person's fundamental cheerful, optimistic nature. Often contrasted with 根暗 (ねくら), meaning innate gloominess.
Antonyms: 根暗
彼女はネアカだから、いつも周りを明るくする。
She has a sunny disposition, so she always brightens up the people around her.
ネアカな性格は、友達を作るのに役立つ。
A cheerful nature helps in making friends.
noun
innately cheerful person; happy-go-lucky person; natural optimist
Refers to a person who is fundamentally cheerful and optimistic. Often used in casual conversation to describe someone's personality.
うちのクラスにはネアカが多くて、毎日楽しい。
There are many cheerful people in our class, so every day is fun.
彼は根っからのネアカで、落ち込んでいるのを見
He is a natural optimist through and through; I've never seen him down.
Compound of 根 (ね, root/nature) and 明 (あか, bright). The word likely originated as slang contrasting with 根暗 (ねくら, root-dark). The exact derivation is uncertain, but it is now a common colloquial term.