1. What does it mean?
차애 is the person or thing placed just after your 최애 in your own favorites. In a fan conversation it commonly refers to the second-favorite member of a group.
Also written or said as chaae, cha-ae
2. The nuance
It describes a preference, not an official role or ranking of talent. It is not always identical to English fandom's 'bias wrecker,' which can mean someone challenging your top choice rather than a settled second favorite.
3. Examples
“최애 포카는 이미 있어서 이번엔 차애 포카를 골랐어.”
I already had my favorite member's photocard, so I chose my second favorite's this time.
“노래마다 눈에 들어오는 멤버가 달라서 차애를 못 정하겠어.”
A different member catches my attention in each song, so I can't pick a second favorite.
Sources
DukPlace: K-pop fandom glossary
References support the meaning and usage. Example sentences are written for NoCapWiki.