So, Seishirou was a human servant and got turned by Natsuno and given an order to kill Kirishiki, but he forgot to add "not yourself", what was a twist.
Seishirou came from a bad household, Chizuru killed his parents but didn't knew or willingly let him be human so they can use his wealth and suck his blood whenever they want it.
He had a strong detachment from own place, something can Shiki to turn into one and it certainly did.
Seishirou was in unrequited love with Chizuru, but she frequently cheated on him with younger men without any restraint and he thank Chizuru for what all she did. What a cuck
Just "love" the hypocrisy of Megumi here, it's okay for her to do awful things, but not to her
Hypocrisy of Sunako, doesn't want die, but has no problem to kill everyone.
Tomio is maybe too extremely traditional, something a rural townsfolk tend to be, but honestly some things he disliked are, reasonable as the changes were far too the worse, especially the comedic funeral.
Tomio final descipline of his bratty son Atsushi, far too late because his killing spree he did after turning into Shiki, seeing how extremely unhinged his son was.