A key characteristic could be the vampire's reclusive nature, much like a hikikomori. Vampires often live in seclusion, away from the normal human society in these novels.
I don't have the exact name of the person who created the Omori manga at hand. It could be worth doing a search on manga databases or asking fellow manga enthusiasts for the answer.
Omori is purely fictional. The story and characters were imagined by the creators, not drawn from real-life events. It offers a fantastical and imaginative experience for players.
At the moment, there's no definite date for the Omori manga release. But you can follow the official social media accounts or manga forums for any potential news or leaks.
One common theme would likely be isolation. If someone has been a hikikomori for 10 years, they are cut off from the outside world, and this would be a central aspect in the story. It could show how they deal with the lack of human interaction on a daily basis.