So MAL adds 41-second promotional videos to the website? That's kind of weird, in my opinion, but this is from one of my favorite series so couldn't miss the opportunity to write a Top Quality review!
All you get from the promotional video is that some girl is missing and happens to be the MCs precious imouto (little sister) and that somehow a new hope was born. You don't really get any of the game's information from the promotional video, but it's basically what I assume to be a money grab side story of the main story that you can play on your mobile
device. It seems to feature a new set of main characters, but it seems possible to get/play the old chars in the game.
The game has only been released in Japan at the current moment. The developers made it so you would need to have a Japanese google account in order to download it from the google play store (not familiar with iOS, sorry). It will supposedly not work unless you've downloaded it from google play.
You don't really get any of the new characters' info from the promotional video. The cast looks a lot less appealing and more generic than the original cast.
Voices seem done very well. Music is very good.
Enjoyment: I mean, it was interesting... I guess...?
Seems like a pretty average promotional video with shaft graphics. I'll probably check out the game just to see what the side story is about, but you might have a bit of trouble if you can't understand Japanese.