Oh.
Right after reading this comment, I contacted the author.
Does anyone know how to contact him directly if he is not online?
If he does not respond in 1 week, we will remove the game from store.
Btw, to avoid this legal situation, we decide to develop story ourself (luckily, after this post, an author contacted to me)
And, thank for being nice to us. (You are always nice) We know we have a lot of defects, and we will correct it.
Thank you so much