According to this, filming has already finished. http://www.wowow.co.jp/drama/original/index.html The official site doesn't list a date though. Just that the drama is happening. The two official articles released (the one in OP and this post) don't list any dates or even a range. It seems like WOWOW (kinda like HBO in Japan, its not a free channel) airs one original drama a month. There are already dramas set for this month, July, and August and another set for "fall 2017". Im thinking we'll get a winter release for Kai's drama tbh. Maybe November or December? It's all filmed though so i guess its all post-production rn.