noun
nihilist
A person who adheres to nihilism, the rejection of all religious and moral principles, often in the belief that life is meaningless.
彼は虚無主義者で、人生に意味はないと考えている。
He is a nihilist and believes that life has no meaning.
虚無主義 is the philosophy of nihilism, while 虚無主義者 refers to a person who follows that philosophy.
Compound of 虚無 (kyomu, 'nothingness') + 主義 (shugi, 'doctrine') + 者 (sha, 'person'). The term is a calque from Western philosophy.