expression, noun
champion of justice; knight in shining armor; crime avenger; hero; superhero
Set phrase often used in fiction, anime, and tokusatsu to describe a righteous hero who fights evil. Can be used seriously or playfully.
彼はまるで正義の味方のように悪者を倒した。
He defeated the villains just like a champion of justice.
子供の頃、正義の味方になりたかった。
When I was a child, I wanted to be a superhero.
Compound of 正義 (justice) + の (possessive particle) + 味方 (ally, supporter). Literally 'ally of justice'.