1.
successor, replacement
A person who takes over someone else's position or role after they leave. Informal in tone and sometimes carries a slightly negative or opportunistic nuance. Originally referred to someone who takes the place of a divorced or deceased spouse.
Etymology
Literally "the pot after" (後 + 釜). Originally referred to the cauldron placed on the fire pit after the previous one was removed. The meaning extended to a person who replaces another in any position.
Usage
Informal. Common in the pattern 後釜に座る (to take someone's place) or 後釜を狙う (to aim for someone's position). Can carry a negative nuance of opportunism. For more formal contexts, 後任 (successor) is preferred.