This is a vampire series and you're all here salty towards them being "murderer"...people read too much fairytales..
Well, there are different kinds of vampire series for different tastes.
It is pretty interesting to contrast it with the other vampire yuri series being scanlated at the moment, Seifuku no Vampiress Lord. That series actively steers away from every possible source of drama and angst as soon as it comes into view, remaining a light-hearted comedy where being a vampire is honestly kind of a sweet deal and doesn't have to involve doing serious harm to anybody.
Meanwhile, in Vampire-chan x Junior-chan, both the vampire and the bride are subject to a combination of biological necessity and chemical mind control to lock them into a codependent dynamic that'll inevitably kill the bride within a year, after which the vampire has to find a new bride and do the same thing all over again, with no way to break the cycle as long as the vampire exists. It's a bleak, hopeless situation for everyone involved, and I'm honestly half expecting Iris to attempt suicide at some point now that she knows just how bad things are.