It's possible that all of these human side characters are going to be "helping" Kou fall in love with Nazuna within his strict 1 year time frame so he doesn't get murdered for being in on the vampire conspiracy. I am still not sure what to make of this whole "Cake or Death" thing, but i don't think introducing more characters is necessarily a bad call if the author wants a longer serialization, as long as he manages to make them interesting. At the moment... they do not really leave much of an impression compared to the characters from Dagashi Kashi.