Watanabe Marie was an AKB48 Kenkyuusei. She joined AKB48 as Kenkyuusei on 26 May 2007 and graduated from AKB48 Kenkyuusei on 15 November 2007. She only participated in two theater performances during her time as an AKB48 member. She ties with Ishibe Aya for having the fewest theater performances of any AKB member. She debuted as an AV actress under the name Mizushima Nana (水嶋那奈) in August 2018.
