I'm not entirely sure specifically what 'oni uta visual novel' is about without more context. It could potentially be a visual novel related to oni (which often refers to demons or ogres in Japanese culture) and perhaps involve a story, characters, and interactions within that theme.
The exact origin of when oni first appeared in stories is hard to pinpoint precisely. But they have been a part of folklore and myths for centuries in various cultures.
Well, in many fanfictions, their relationship often develops through shared experiences. For example, they might go through tough times together, like dealing with threats to their family or the Earth. These experiences bring them closer and make their kisses more meaningful, as they represent a deeper bond formed through adversity.
Some possible unique features in 'ao oni visual novel' could be its use of sound. Since it's about something like 'ao oni' which might be a bit spooky, the sound effects and music could be really immersive, creating a very eerie atmosphere. Also, the character interactions might be unique. If the 'ao oni' is a main character or an antagonist, the way the other characters interact with it could be different from other visual novels. For example, the dialogue choices when facing the 'ao oni' could be very intense and have high - stakes consequences.
Since it's a visual novel related to oni, it could have unique features such as a special combat system if there are battles with oni in the story. Also, the cultural elements of Japanese oni might be presented in a unique way. For example, the use of traditional Japanese music or sound effects to enhance the oni - related atmosphere. The dialogue might also be unique, with the oni having their own way of speaking, perhaps more rough or archaic - sounding. And the story structure could be centered around the characteristics of oni, like their love for chaos or their hierarchical society if that's part of the plot.
I haven't heard about this 'oni and the great bird' story before. It would be great if you could give some more details like where you heard about it, or if there are any key elements in the story that you can remember. This would help me to better answer your question.
As I'm not aware of the actual 'oni and the great bird' story, it's difficult to say for sure. However, in general, in a story named like this, the oni, which is likely to be some sort of supernatural being, and the great bird are likely to be the central figures. There may also be characters related to the environment they are in, like people living in the area where the oni and the bird interact, or other magical creatures if it's a fantasy - style story.