Perhaps they are drawn to the drama, romance, or adventure elements present in the manga. It's hard to say exactly, but there could be multiple reasons for their obsession.
It could be that your actions or personality in the manga have made a deep impression on them. Or perhaps there's some underlying story or plot device that explains their obsession.
Maybe it's because you have some unique qualities or traits that draw their attention and interest.
Perhaps your presence in the manga or anime creates a sense of mystery or intrigue for your in-laws. It could also be that your relationships and interactions with others are highly engaging and they can't help but be obsessed.
It might be that they are really attached to you and think highly of you. Maybe they have a lot of free time and focus too much on you. Or it could be that they are trying to figure out how to have a better relationship with you and go a bit overboard.
Maybe they see something special in you that catches their attention.
It could be that your actions or behavior have made a deep impression on them. Or perhaps they see something in you that they admire or find fascinating.
It could be that your actions or personality have made a deep impression on them. Or perhaps there's some underlying plot reason within the manhwa's story that explains their obsession.
Maybe it's because you have some qualities or traits they really admire and find fascinating.
It could be that you've shown kindness or done something remarkable that caught their attention and made them obsessed. Or perhaps they have their own reasons related to their personalities and expectations.
Maybe they see something special in you that attracts their attention and interest a lot.