Tsukamoto Mariko made her theater debut on her 38th birthday on July 16th. She performed with Team 4 in their current stage show [Idol no Yoake] and centered the unit [Kataomoi Taikakusen]. She had already appeared at several AKB48 shows and concerts but her theater debut came only now, three months after she joined.
One day before this debut Tsukamoto Mariko had already announced her graduation in a Papico CM which did not come as a surprise since she was only a temporary member for the time period of the Papico campaign (until August 31st).
The graduation announcement CM can be watched on the Papico homepage: http://papico.glico.com/cm/14otona_cm5_30b.html