In 2014, a Gackt-focused dating sim based on his song of the same name was released on iOS and Android.
From what I can tell, it had various chapters involving Gackt in different roles, including a doctor and your childhood friend (yes, really). The .apk is still available online, but it no longer functions after the game's servers were shut down in December of 2015, according to the official twitter.
I have no idea how to unpack .apk files, so I don't know how much of the game is contained in the actual files and how much was online, so in those regards I'm sorry for the lack of information. The game was free to play, with in-app purchases apparently, during the time it was up, and the apk can still be found for download on apk sites like apkpure.com/p-s-i-love-u-gackt/jp.gacktapp.gackt. (if a link like this is against site rules, please let me know and I will remove it.)