This is about purely good character(s). They are completely and utterly incorruptible. The natural bane of The Corrupter, and immune to The Corruption.

While the people around them can be tempted by power, fame, sex, money, or love, this character is immune to succumbing to temptations. More rounded characters may feel the temptation and still resist. They will always do the right thing for the greater good, if not necessarily the nice thing, at times even if violencence is necessary. 

source: https://tvtropes.org/pmwiki/pmwiki.php/Main/IncorruptiblePurePureness