The Durarara novels often have complex characters. For example, characters like Izaya Orihara are full of contradictions. His actions are unpredictable, and his motives are often shrouded in mystery. This makes the novels very engaging.
I'm not entirely sure as I haven't read it specifically. But generally, a light novel often involves unique characters, a fictional world, and an engaging plot. It might be about a Dullahan, which is a headless horseman - like figure in Irish folklore. So perhaps it has elements of mystery, adventure, and the supernatural related to this Dullahan character.
The Dullahan is a headless female figure in Irish folklore. A Dullahan girl story might involve her spooky rides on a black horse, holding her own head. She is often seen as a harbinger of death. Legend has it that when she stops riding, someone is about to die. She can also cross water, which is unusual for many other spectral beings. Her appearance is terrifying, with a very pale body and a head that has a ghastly expression when she holds it up.
The Dullahan is a headless horseman in Irish folklore. The first dullahan stories might be about its origin. Maybe it was once a mortal who was beheaded in a cruel way and thus became this spooky figure. It could also be about its first appearances in certain areas of Ireland, scaring the locals with its headless form on a horse, carrying its own head under its arm.
One key element is the headless appearance of the girl. It makes her extremely spooky. Another is her black horse, which she rides swiftly. Also, the fact that she holds her own head is a very characteristic element.
One common theme is the isolation of the female dullahan. Since she is often different from the normal beings in the fictional world, she is usually isolated. For example, in many stories, she is shunned by humans because of her appearance and the fact that she is a supernatural being.
Often, the main characters can include the Dullahan themselves. They are usually unique in appearance, with their headless form being a distinct feature. Another main character could be Ruby, as she is one of the central figures in RWBY and might interact with the Dullahan in various ways, like in combat or during a mission.
I'm not sure specifically as I haven't read 'dullahan first stories'. But generally, stories could be about the dullahan's origin, its encounters with humans, or its role in a particular folklore or fictional world.