If you look into all GNW ninjas this version have now you will notice that Sai and Tenten are event gain while the rest are check in rewards.
So far we already got Shino, Kiba, Neji, Kankuro so my bet is Choji next month. After that I think we might receive a big update as well as new check in monthly rewards.
Or they just recycle old GNW ninjas, who know lol