As of now, Uta is indeed alive. The story hasn't depicted anything otherwise. Maybe there'll be changes in the future, but for now, Uta's part in the manga continues with them being alive.
Their relationship could start with Uta being initially distrustful of Luffy. After all, Luffy is a pirate and Uta has her own ideas about pirates. But as she sees Luffy's pure heart and his determination to protect his friends and pursue his dreams, she starts to warm up to him. They might then become friends who share their different stories and experiences.
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.
Saya no Uta Visual Novel is often known for its distinct narrative. It might include elements like complex character relationships, a particular setting, and a series of events that the player gets to experience. It could be about a journey, a mystery, or some sort of emotional exploration, but again, this can vary depending on the specific content of the visual novel.
I would recommend 'Uta's Hidden Affection'. In this fanfiction, the development of the relationship between Uta and the reader is really interesting. It starts with small interactions that gradually build into something deeper. The description of Uta's character is very accurate to his original personality in the source material.