How Long Does It Take to Watch Engaged to the Unidentified?

Not every girl gets what she wants on her 16th birthday, but Kobeni's gift is something she never saw coming: an arranged marriage! Thanks to her late grandfather, Kobeni's been engaged to a total stranger since childhood, and even though she's supposedly met him she doesn't remember a single thing about him. Even weirder is that both her Mom and creepily over-doting sister, Benio, seem completely unsurprised when the groom-to-be, Hakuya, and his younger sister, Mashiro, show up on the family's doorstep to move in with them!

But it's not until they start attending Kobeni's school that things take an even stranger turn after she starts to pick up some very... unusual vibes from her potential future family. From Mashiro's obsession with aliens and UMAs (Unidentified Mysterious Animals) to Hakuya's disconcerting lack of emotion, there's something very off about them that Kobeni can't quite put her finger on. What has her grandfather gotten her into, and how does this relate to the strange gap in Kobeni's memory?