The title refers to Bellamy's sense of responsibility for Octavia. The phrase is based on Genesis 4:9 where Cain asks God "Am I my brother's keeper?" The popular use of that phrase is to disavow responsibility for "looking out for" someone else.
Monique Ganderton, who plays Aurora Blake, is 4 years older than Bob Morley and 6 years older than Marie Avgeropoulos.