noun
critical friend; friend who gives frank advice
A friend who is not afraid to point out your faults or argue with you for your own improvement. The term is somewhat formal and not an everyday word; it carries a classical Chinese flavor.
彼は私にとって、遠慮なく意見を言ってくれる争友だ。
He is a critical friend to me, someone who gives his honest opinion without reserve.
真の争友を持つことは、自己成長に欠かせない。
Having a true critical friend is essential for personal growth.
From Chinese 爭友 (zhēngyǒu), literally 'contending friend'. The Japanese reading そうゆう is the on'yomi of the characters. The concept is rooted in Confucian ideals of friendship where a true friend is one who dares to remonstrate.